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Volume 2012 (2012), Article ID 853123, 17 pages
Host Defence against Bacterial Biofilms: “Mission Impossible”?
Institute for Immunology, University of Heidelberg, 69120 Heidelberg, Germany
Received 11 September 2012; Accepted 4 October 2012
Academic Editors: C. Faveeuw, D. Lilic, P. Puccetti, and A. Taylor-Robinson
Copyright © 2012 Gertrud Maria Hänsch. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Bacteria living as biofilms have been recognised as the ultimate cause of persistent and destructive inflammatory processes. Biofilm formation is a well-organised, genetically-driven process, which is well characterised for numerous bacteria species. In contrast, the host response to bacterial biofilms is less well analysed, and there is the general believe that bacteria in biofilms escape recognition or eradication by the immune defence. In this review the host response to bacterial biofilms is discussed with particular focus on the role of neutrophils because these phagocytic cells are the first to infiltrate areas of bacterial infection, and because neutrophils are equipped with a wide arsenal of bactericidal and toxic entities. I come to the conclusion that bacterial biofilms are not inherently protected against the attack by neutrophils, but that control of biofilm formation is possible depending on a timely and sufficient host response.
Since the seminal work by Bill Costerton and the effort by many more scientists, bacterial biofilms have emerged as a novel pathogenic principle, particularly of opportunists causing persistent and in part destructive inflammatory process in man and in animals [1–7]. Over the years it became increasingly clear that bacteria (and also fungi) form ordered, well-organised communities, embedded in a slimy material that is produced by the bacteria. Because of the slime, biofilms are occasionally even visible to the naked eye (example in Figure 1).
Biofilms were actually first described for water-dwelling bacteria in their natural environment and later on recognised as problem-causing “biofouling” agents in water-dependent industries, such as paper mills, or on boats . There is a general agreement that living in biofilm was of advantage for the bacteria particularly when nutrition was scarce and the environmental conditions were unfavourable [9–11].
Scarce nutrition, however, is most likely not the reason that drives biofilm formation in the human body. There, the host’s defence mechanisms might exert an evolutionary force that drives opportunists to acquire pathogenic factors or other protective means. Mucosal biofilms, for example, are colonising the colon. As “commensals” they are minding their own business and do not interfere with host functions. Moreover, they apparently escape detection and do not elicit an adverse response [12, 13]. Biofilms at other sites were recognised as the ultimate cause of persistent and destructive infections and inflammatory processes. Because inflammation indicates activation of an immune response, the latter observation leads to the questions how the immune system recognises and reacts to biofilm infections. This paper will focus on possible interactions between bacterial biofilms and innate host defence mechanisms, particularly the interaction of phagocytic cells with biofilms.
There are excellent reviews on biofilm formation in the literature (e.g., [14–16]) and on a very informative website of the Center of Biofilm Engineering (http://www.biofilm.montana.edu/) for further reference; therefore I will touch the issue of biofilm formation only briefly and only as far as it is required for the general understanding.
2. Bacterial Biofilms: No More Lone Rangers?
Examples for biofilms are shown in Figure 1. Even without a microscope the slimy mass can be recognised, which in this particular case consists of Staphylococcus aureus, surrounded by the slime, scientifically referred to as extracellular polymer substances (EPS, in the older literature also called extracellular matrix).
Biofilm formation is the result of a genetically driven process that alters the behaviour of the individual bacterium. It starts with attachment of bacteria to a surface (or to each other). Bacteria lose their motility and acquire—among others—the ability to produce and release materials for the EPS. The process is controlled by the so-called quorum-sensing molecules, which are produced and released by the bacteria and hence are also known as “autoinducers” [17, 18]. The very basic process of biofilm formation appears to be similar for all bacteria, on the molecular level; however, great differences exist. Biofilms have distinct, species- and occasionally even strain-specific properties. The composition of the EPS differs greatly among the species and might even vary depending on environmental and culture conditions. Moreover, different species use different quorum-sensing molecules, whereas some are shared with others (those of P. aeruginosa with other Gram-negative bacteria).
An almost philosophical question is what drives bacteria into forming a biofilm. In natural surroundings it could be shared food resources, protection from predators and unfavourable conditions, and also an easier exchange of genomic material [19–21]. Very possibly, living in a biofilm is not the exception, but the preferred life-style of bacteria and single, free-floating bacteria could only be an experimental artefact generated by culture. If so, our perception of host-pathogen interaction has to be reconsidered, as have our techniques to isolate and propagate bacteria for diagnostics purposes, or to determine susceptibility to antibiotics and biocides. The latter is extremely relevant, because bacteria in biofilms acquire a relative resistance towards antibiotics and biocides [22–25]. Moreover, bacteria living as biofilm in vivo might escape detection by standard microbial diagnostic methods, giving false-negative results [26–28].
3. Bacterial Biofilms as Pathogen
As pointed out above, especially bacteria that are considered “opportunists” become pathogenic when organised as biofilm. Well-studied examples are Pseudomonas aeruginosa, and P. cepacia which are known as pathogens of immunocompromised or immunodeficient patients [29, 30]. Biofilms of P. aeruginosa and Burkholderia cepacia contribute to chronic infections in patients with cystic fibrosis [31–35], or nonhealing wounds [36, 37]. Other chronic infections could be attributed to biofilms, for example, otitis media , periodontal disease [39, 40], rhinosinusitis , and skin infections [42, 43]. Biofilms might consist predominantly of one bacteria species, but others of mixed populations  (reviewed in ).
Especially well studied with regard to biofilm formation are the so-called device-associated infections. Artificial surfaces, particularly indwelling catheters or tubing, may be colonised by bacteria, particularly by P. aeruginosa or staphylococci species and spread from there [46, 47]. One explanation is that the bacteria preferentially adhere to artificial surfaces—as opposed to inner surfaces covered with epithelial cells [48, 49]. A rather intriguing explanation is that epithelial cells might actively prevent biofilm formation, for example, by inactivating the autoinducers participating in biofilm formation [50, 51]. In line with an active role of epithelial cells is the observation that patients with impaired epithelial function (patients with cystic fibrosis or ciliary dyskinesia syndrome) have a high risk to develop chronic bacterial infection [52–55].
4. Implant-Associated Osteomyelitis: A Prototype of Biofilm Infection
To analyse the immune response to biofilm infection, our group has focussed on the so-called implant-associated osteomyelitis, a persistent bacterial infection caused by formation of bacterial biofilms on endoprostheses or on osteosynthesis materials, such as screws, plates, or nails. Infection of implanted material is a major complication of orthopaedic and trauma surgery, which as last and devastating consequence could result in functional impairments of the extremity and even in their loss (reviewed in [56–59]). Depending on the circumstances and individual risk factors of the patient, the incidence of infection ranges from 1 to 6 infection per 1000, which, considering the ever increasing number of patients requiring endoprostheses, amounts to many patients and increasing costs [60, 61] and explains the clinical and scientific interest in this condition .
Implant-associated osteomyelitis is particularly well suited for studying the local immune response, because the infected implant has to be removed, the infected site becomes accessible: infiltrating immunocompetent cells can be recovered and characterised ex vivo, and also tissue can be obtained for further analysis (an example is shown in Figure 2). Moreover, besides the infection, the patients do not suffer from diseases that might affect the immune system.
5. The Local and Systemic Immune Response in Patients with Implant-Associated Osteomyelitis
Fever and increase of C-reactive protein concentrations and of leukocyte count in the peripheral blood are established parameters for infection. In implant-associated osteomyelitis, those systemic reactions do not occur regularly; in approximately 100 patients we observed over the last years, only 20% presented with enhanced leukocyte count and 40% with enhanced C-reactive protein concentrations. The local reaction, however, was impressive: in all patients leukocytes were found at the infected site, predominantly PMN (50 to 70%), to a lesser degree T-lymphocytes (5 to 20%), NK-cells (5%), and a few monocytes. The cells were highly activated. Neutrophils upregulated adhesion proteins (CD11b, CD18), Fc-receptors MHC class II molecules , or the chemokine receptors CXCR6 . Also functionally, the PMN were altered: enhanced production of oxygen radicals was seen, and a reduced chemotactic activity .
The infiltration of T cells was somewhat unexpected, because at least according to the common immunological point of view, T cells are not directly involved in the defence against bacteria. In the local wound lavage of our patients, however, T cells were apparently activated, particularly CD8+ cells, and some also expressed pattern recognition receptors, which to some degree explains how these cells recognise bacteria [66, 67].
Analysis of tissue samples from patients with implant-associated osteomyelitis confirmed the findings: in areas of bone degradation, PMN were abundant, some lymphocytes and monocytes were seen, as were osteoclasts, the latter, as expected, particularly next to the bone and in resorption lacunae (example in Figure 3). A correlation of neutrophil density with the number of osteoclasts was calculated in a study comprising patients with osteomyelitis, supporting the notion that the infection and the ensuing proinflammatory microenvironment may promote osteoclastogenesis and bone resorption .
Infiltration of proinflammatory cells, particularly of PMN, was also seen in other biofilm infections. Particularly well studied is the P. aeruginosa infection in patients with cystic fibrosis or with chronic, nonhealing wounds . Infiltration of neutrophils indicates that the immune system has reacted to the infection in an appropriate manner, leading to the question how the infiltrated cells will now interact with the biofilm.
6. Bacteria and Bacterial Biofilms from the Viewpoint of the Host
The host defence discriminates between pathogens and commensals, so colonisation with bacteria does not necessarily elicit an immune response. With our intestinal “microflora” and our skin germs we live in mutual acquiescence. There is even evidence that those bacteria modulate and shape our immune system from early childhood throughout the whole life [69–72]. The bacteria are tolerated because they reside in privileged areas of immune tolerance. This compartmentalization allows a local, but not systemic immune response. The epithelial cell layer and the cytokine micromilieu are essential to maintain compartmentalization. Changes in the composition of the human commensal bacterial microflora could enhance the susceptibility to allergic diseases . Disruption of the epithelial barrier or invasion of bacteria by other means will perturb the friendly coexistence and will activate a host response.
Invading bacteria encounter an intricate and complex host defence system. Different cells, numerous cellular receptors, signalling pathways, and effector molecules have been identified, which recognise potential dangerous invaders and execute their elimination. This diversity is needed because different bacteria species also differ with regard to their susceptibility towards the host defence (there are numerous excellent reviews that can be used for reference; e.g., [73–75] to name a few).
With an intact immune response, many infectious agents are eliminated without being noticed by the host; we only know from immunocompromised or immunodeficient hosts how frequent infections really are.
6.1. PMN as “First Line Defence”
I focus here on PMN, which are usually the first cells to arrive at a site of bacterial infection and hence are often referred to as “first line defence.” That PMN are crucial for the host defence against bacteria is supported by the fact that lack of PMN (neutropenia) or congenital defects of PMN result in an enhanced risk to develop life-threatening infection (reviewed in [76–78]).
Prerequisite for the host defence is the ability of PMN to sense a localised infection, to emigrate from blood vessels, and to migrate actively through the tissue to the site of infection. This process is very well controlled and has been unravelled over the years [79–81]. Numerous factors have been identified that can attract neutrophils, notably cytokines (reviewed in [82–84]). Of interest, also bacteria-derived products might serve as chemoattractants. The most prominent example is f-Met-Leu-Phe, a tri-peptide that was generated according to naturally occurring formyl peptides [85–87]. We and others also described a chemotactic activity for N-(3-oxy dodecanoyl) homoserine lactone, a quorum sensing molecules derived from P. aeruginosa [88–91] (see the following).
Once arrived at the infected site, PMN take up bacteria by phagocytosis. Bacteria may be killed via generation of reactive oxygen species (ROS). The relevance of ROS as bactericidal principle is shown by genetic defects within the cascade leading to ROS generation (chronic granulomatous disease, CGD). The patients suffer from often severe and recurrent bacterial and fungal infection and rely on life-long treatment with antibiotics, if causal therapy is not possible [78, 92, 93].
PMN contain also a number of other cytotoxic or bactericidal substances, which might act intracellularly or extracellularly (reviewed in [94, 95]). The significance for the host defence of many of these entities is not yet apparent. Presumably, they have more or less specialised functions or targets, which remain to be identified. In the context of biofilm infection, lactoferrin is of special interest, because aside from its bactericidal activity, it also prevents biofilm formation as shown for staphylococci species [96, 97] (see the following).
As local defence, there is also an arsenal of the so-called cationic antimicrobial peptides (CAMPs) including defensins, cathelicidins and thrombocidins, which are partly contained in neutrophils, but also in epithelial cells and others [98, 99]. Their bactericidal potential is limited due to countermeasures of the bacteria ; with regard to biofilm clearance, for the cathelicidin LL-37, an inhibitory effect was described (see the following).
6.2. How PMN Recognise Bacteria
PMN are considered as “non-specific” or “innate” effector cells, meaning that they do not recognise bacteria in an antigen-specific manner and that they do not generate memory responses. Rather, PMN sense evolutionary conserved surface molecules that are shared by many bacteria species. Numerous receptors recognising those conserved structures as “foreign and potentially dangerous” and therefore referred to as pathogen-associated molecular patterns or microbe-associated molecular patterns (PAMPs or MAMPs) have been identified. Among those are the so-called Toll-like receptors, which are found on all immunocompetent cells. In humans, the family comprises 9 receptors, which differ with regard to their target structures, which include lipopolysaccharides, lipoteichoic acid, peptidoglycan, flagellin, and others (reviewed in [101–103]). Toll-like receptors appeared early in evolution and were probably the first receptors to distinguish between “self” and “microbe” [104, 105]. Aside from Toll-like receptors, also other pattern recognition receptors are known. CD14, for example, recognises lipopolysaccharides [106, 107], the so-called scavenger receptors bind other microbial constituents, such as complex carbohydrates [73, 108, 109]. PMN also recognise bacterial DNA. This is relevant when considering the host defence against biofilms, because DNA is part of the extracellular biofilm substance and is required for efficient biofilm formation [110–112]. Toll-like receptor 9 was described as a DNA receptor , but PMN react to bacterial DNA also independently of TLR9 [114–116].
So it appears that PMN and also the other phagocytic cells express a wide array of receptors which by themselves or in combination with each other sense bacteria and may then elicit an adequate response . Adding to the complexity is the fact that for many bacteria species clearance from the circulation and efficient phagocytosis and killing depends on “opsonisation,” that is, on coating of bacteria with antibody and complement (complement C3b/C3bi) [118–120]. Receptors for immunoglobulin G (CD16, CD32, and following activation also CD64) mediate phagocytosis and intracellular killing together with the complement receptors (CR1, CR3). There is an abundance of literature on the dependence and efficiency of phagocytosis induced by Fc-receptors, complement receptors or a combination thereof and also a combination of Fc-receptor with other receptors [74, 121–125], and, as expected, escape mechanisms of the target bacteria [126–128]. An important caveat is that the majority of data describing phagocytosis by PMN or other phagocytic cells are derived from experiments using planktonic, that is, “free-swimming,” bacteria. As I will explain in more detail in the following, the situation might be quite different when biofilms are considered.
6.3. How PMN Interact with Biofilms
Neutrophils (and other phagocytic cells as well) are often compared to single cell organisms such as Dictyostelium discoideum, because migration and phagocytosis are redolent of chasing and trapping of a prey [129–131]. Although the analogy is arguable on a molecular level, neutrophils might be regarded as predators and—to carry the analogy further—bacteria as prey. Observing the interaction of PMN with a staphylococci biofilm emphasizes this impression (see video clips in supplementary material available online at doi:10.5402/2012/853123).
Also seen from the video clip is that the PMN attack the bacteria and the extracellular substance/EPS, the slime, as well. The EPS is not a massive impermeable wall, but rather a hydrogel-like structure, composed of exopolysaccharides and proteins, dead bacteria, bacterial DNA, and enzymes. Composition and structure of the EPS varies widely among the bacteria species, and even within one species, there are strain-specific properties. For P. aeruginosa, for example, mucoid strains have been isolated from patients with cystic fibrosis, which produce alginate as a major EPS constituent, whereas strains of other origin do not (for review see [132–134]). So when considering the interaction of neutrophils with biofilms or EPS, respectively, the findings need to be interpreted with caution as they might not be true for biofilms of other species and not even for biofilms from the same species, because also culture conditions affect biofilm properties. Culture dishes versus polystyrene used for catheters or metals which are used for implants can make a major difference, particularly with regard to the initial uptake of the bacteria. Also the application of the in vitro findings to the in vivo situation or from the animal model to human disease is rather challenging, because the “models” usually do not reflect exactly the naturally occurring disease; moreover, the experimental animals do not react necessarily similar to human. Mice, for example, have less neutrophils compared to humans (on average only 20% of the leukocytes are PMN), so it is quite possible that the quality of the initial, innate response involves more monocytes and hence differs from the human situation.
The majority of data on the interaction of neutrophils (or other phagocytic cells) with biofilms are derived from studying P. aeruginosa or staphylococci biofilms, the former because it is one of the major infectious agents of hospital-acquired infection, particularly of patients in intense care units who require indwelling catheters and tubing, and also because of its presence and role in cystic fibrosis; the latter as a major cause of implant-associated infection.
Our group is focussed on PMN, but I will occasionally also refer to data obtained with peripheral blood leukocytes or monocytes/macrophages. Monocytes share some functional characteristics with neutrophils but differ in other regards.
6.4. PMN and P. aeruginosa Biofilms
When analysing the interaction of neutrophils with P. aeruginosa biofilms generated in vitro, it was observed that neutrophils settled on biofilms, and they, however, did not move around and exhibited little or no bactericidal activity . Apparently, P. aeruginosa biofilms downmodulated leukocyte functions [136–138]. Subsequent experiments attributed the inhibitory capacity to components of the EPS, particularly to alginate, a high molecular weight, acetylated polymer composed of nonrepetitive monomers of β-1,4 linked L-guluronic and D-mannuronic acids. In vitro, alginate inhibited phagocytosis  and directed migration of PMN . Together, these data point to a role of EPS components as a defence mechanism against immunocompetent cells.
Data derived from patients with cystic fibrosis confirm that notion: initially, the lung of the patients is colonised by nonmucoid strains. When the disease progresses, mucoid phenotypes emerge, which produce alginate, which in turn is linked to structural changes of the biofilm and results in a worsening of the clinical prognosis [32, 141, 142]. Thus, although alginate is apparently not required for biofilm formation in the first place, it enhances the resistance towards the host defence .
Rhamnolipids were identified as further extracellular components with the potential to fend off the leukocyte attack. Rhamnolipids are amphiphilic molecules composed of rhamnose and hydrophobic fatty acid moieties and are also known as the heat-stable hemolysin of P. aeruginosa .
Rhamnolipids are produced by P. aeruginosa upon biofilm formation. The synthesis is controlled by quorum-sensing molecules [144, 145]. Their apparent physiological function is the maintenance of the ordered structure of the biofilm, particularly of the fluid-filled channels . Early data by Shryock et al. (1984) and Kharazmi et al. (1989) described an activation of neutrophils or macrophages by low doses of rhamnolipids and lytic, necrotic cell death in higher concentrations [147, 148]. Eventually, the cytotoxic potential of rhamnolipids was linked to the pathogenicity of P. aeruginosa biofilms: rhamnolipids could actively fend off the neutrophils, leading to persistence of bacteria; moreover, lysed neutrophils may release their content of proteolytic enzymes, which may cause tissue damage, and hence progression of the inflammatory response [149–151]. Elastase derived from neutrophils was considered a major pathogenic agent [152–155], a presumption supported by the fact that elastase and cellular debris of neutrophils are found in the sputum or the bronchial lavage of patients with cystic fibroses [155–157].
An interesting aspect is that the bacteria react actively to the neutrophil attack. In response to PMN, the rhamnolipid synthesis is upregulated, which means that P. aeruginosa recognises PMN . How this type of interkingdom signalling works is not yet known. Possibly, cytokines derived from the infiltrating neutrophils are recognised by the bacteria. That this is possible in principle had been shown for cytokines such as tumour necrosis factor α, interleukin 1 and 6, respectively, which do promote bacteria growth [159–161]. Moreover, interferon-gamma has been implied , but because interferon gamma production by neutrophils has been shown only in mice, other candidates have to be considered in humans.
In summary, P. aeruginosa biofilms have various means to counterattack the immune defence, which—at least in part—explains their persistence.
7. Neutrophil-Derived Mediators with the Potential to Prevent Biofilm Formation
So the question arises, whether or not the host has any means to destroy or prevent the generation of P. aeruginosa biofilms. As with many other infectious agents, I think, the success of the host defence is a matter of timing. Established biofilms might be difficult to attack; there is, however, evidence that prevention is possible. Lactoferrin, which is stored preformed in neutrophils but is also present in numerous external secretions, is able to prevent biofilm formation. The effect was attributed to the ion-chelating capacity of lactoferrin, which, however, might not be the only mechanism [97, 163, 164]. Decreased levels of lactoferrin might predispose to biofilm infections, as suggested for patients with chronic rhinosinusitis . In line with these data, decreased lactoferrin concentrations were also observed in patients with cystic fibrosis. An enhanced cleavage of lactoferrin by the protease cathepsin B was described, which resulted in loss of bactericidal and antibiofilm activity [166, 167]. Because cathepsin B release can be induced by elastase, it is possible that the lactoferrin effect might be abolished in situations where elastase prevails . Nevertheless, the fact that lactoferrin inhibits biofilm formation prompted the question for its therapeutic use, for example, in chronic wounds, where it might be especially useful, because its antibiofilm action is not limited to P. aeruginosa [169–173].
7.2. Cathelicidin: Human Cationic Antimicrobial Protein 18 (LL-37)
LL-37 is the C-terminal part of antimicrobial protein (hCAP18), which is mainly expressed by neutrophils and epithelial cells, but is also found in body fluids. Numerous functions have been ascribed to LL-37, including induction of chemotaxis, angiogenesis, or chemokine secretion. LL-37 is an antimicrobial peptide, that is produced in response to infection, for example, by mycobacteria [174, 175]. LL-37, however, also inhibits biofilm formation by decreasing the adherence of the bacteria, by stimulating their motility, and by downregulating quorum-sensing-dependent genes, required for biofilm formation . An antimicrobial effect of LL-37 was shown in a rabbit model of P. aeruginosa infection , and because the inhibitory effect is not limited to P. aeruginosa, it is attractive to assess its use for therapy of chronic wounds and other biofilm infections [178–181].
8. PMN and Pseudomonas Quorum-Sensing Molecules
A further interesting observation regarding the interaction of P. aeruginosa and cells of the host defence is the fact that immunocompetent cells recognise quorum-sensing molecules. As described above, quorum-sensing molecules are produced by bacteria as autoinducers and participate in biofilm formation. P. aeruginosa produce, among others, N-acetyl homoserine lactones, which also interact with mammalian cells. For N-(3-deoxy-dodecanoyl) homoserine lactone (AHL-12), an immunomodulatory function was described, particularly inhibition of the T-cell activation and induction of apoptosis [182–185]. This so-called “interkingdom signalling” was interpreted as another means of bacteria to evade host defence mechanisms [186, 187]. Data by Vikstrom’s group and ours, however, suggest that AHL-12 might activate the local host defence by stimulating phagocytic cells: enhancement of phagocytosis, upregulation of pertinent surface receptors, and induction of chemotaxis were shown [88–91, 188]. How AHL-12 interacts with the mammalian cells is still under investigation. Free diffusion into the cells, binding to an intracellular transcription factor or to a surface receptor, has been proposed [88, 89, 91, 189–192], as has been the activation of Rac1, of Map kinases, and an independence of the Toll-like receptor activation cascade [89, 91, 192]. Another, not yet answered question is whether or not these in vitro findings are relevant to the infection in vivo (reviewed in ).
9. PMN and Staphylococci Biofilms
Staphylococci have developed numerous active and passive means to evade host defence mechanisms (reviewed in [127, 194–196]), and biofilm formation is just one of those. Depending on the experimental system, biofilm formation might not be “superior” to the other strategies [197–199], which explains to some extent the apparent inconsistency of data and interpretations in the literature.
Host defence against staphylococci biofilms is mainly studied with S. aureus and S. epidermidis, because these bacteria are frequently isolated from patients with osteomyelitis (and implant-associated osteomyelitis) and are thought to be the “ultimate cause” of this chronic and destructive inflammation [2, 200–204].
In vitro data indicate that S. aureus biofilms are not inherently protected against the attack by neutrophils or macrophages. Phagocytosis and generation of oxygen radicals was seen, as was clearance of biofilm and release from the neutrophils of DNA (see also the video clip and Figure 4) [96, 205–208]. When tested under comparable conditions, S. epidermidis biofilms appeared to be less sensitive towards the neutrophil attack, but still clearance of biofilm and phagocytosis was seen .
Of note, in contrast to the situation with planktonic bacteria, phagocytosis of S. aureus biofilms occurred also in the absence of opsonisation with antibody and complement; killing, however, required the additional signal provided by IgG [208, 209]. For S. epidermidis, even coating with complement appears to be required, and preventing complement deposition on the biofilm was suggested as a means to protect the bacteria .
The observation that PMN and other leukocytes adhere to staphylococci biofilms also in the absence of opsonising antibodies suggested that the cells recognise biofilm constituents. Because leukocytes express numerous receptors for microbial patterns, it was obvious to assess their participation in leukocyte binding. So far, these experiments did not yield conclusive results. Using an in vivo mouse model of catheter infection, participation of the toll-like receptors TLR2 (binding among others to lipoteichoic acid) and TLR9 (binding to bacterial DNA) could be ruled out .
Our group is trying to identify molecules within the extracellular substances of staphylococci biofilms that can interact with neutrophils. Entities inducing degranulation of PMN including up regulation of CD11b and release of lactoferrin were found; their further characterisation is still underway .
Whereas phagocytosis and killing of staphylococci is possible in principle, the effector functions might not be very efficient. In vivo experiments in a mouse catheter model indicated that the macrophages were functionally impaired . Previous data by others suggested that the “slime” contains material interfering with the reactive oxygen species, the major cytotoxic entities of PMN and of other phagocytic cells as well [213–216]. The entity within the slime has not yet been identified in these experiments nor has its mode of action.
In subsequent experiments, Vuong and colleagues showed that staphylococci produced an extracellular polysaccharide, the so-called “polysaccharide intercellular adhesin” (PIA) . PIA is crucial for biofilm formation and—as shown in experimental animals—is involved in catheter infection and protects against major components of human innate host defence [218, 219]. An epidemiological study linked the genes responsible for PIA production to infection derived from indwelling medical devices , supporting the notion that biofilm formation, but may be also antihost properties, is required for infection to occur and to persist.
As pointed out above, an important issue when studying biofilm formation is the initial attachment of the bacteria to a surface. Particularly the quality of the surface decides the time course of the attachment. S. aureus, for example, attach more rapidly to metals used for implants and prosthesis compared to conventional plastic culture dishes [48, 221], and biofilm formation occurs also more rapidly on metals, especially of rough surfaces. Therefore, also the susceptibility of the biofilm towards the attack by neutrophils might vary with the underlying material, which to some extent also might explain diverging results.
Interaction of host defence and biofilms is also observed at the level of the quorum-sensing system, which regulates biofilm formation and other virulence factors as well. In S. epidermidis, the agr quorum-sensing system was identified and a peptide signalling molecule (phenol-soluble modulin, PSM) [222, 223]. Apparently, agr or rather agr-controlled events affect the host interactions: agr mutant strains of S. epidermidis were not able to induce cytokine production or chemotaxis of neutrophils  and were susceptible to antimicrobial peptides and oxygen radicals . Essentially similar observations were made for S. aureus, suggesting that the quorum-sensing operon might participate in host defence mechanisms other than biofilm formation .
10. Consequences of a Failed Immune Defence against Biofilms
Infiltration of neutrophils and other immunocompetent cells is a hallmark for biofilm infection and is especially well analysed in cystic fibrosis and implant-associated osteomyelitis (see above). The infection, however, persists, and destructive inflammatory processes are seen, for example, bone degradation in implant-associated osteomyelitis. Very likely, destruction is caused by infiltrating leukocytes, because in the failed attempt to kill bacteria, they might release their bactericidal and cytotoxic entities into the surroundings causing extended tissue damage. This so-called “frustrated phagocytosis” or “failed attempt” could then degrade tissue and generate a proinflammatory environment that attracts more leukocytes, inflammation progresses [227, 228] and eventually results in generation of bone-degrading osteoclasts [229–231]. Inflammation will also proceed, because necrotic or lysed leukocytes are not cleared from the inflamed site. Clearance of neutrophils, that have exerted their bactericidal action, however, is a prerequisite for limiting an inflammatory process in time and spatial manner, whereas the failure to clear spent neutrophils is thought to promote inflammation [117, 232–234]. Clearance of spent neutrophils, however, occurs when following phagocytosis the cells become apoptotic and recognised and taken up by macrophages without spilling their content. In case of biofilm infections, neutrophils might even promote biofilm formation, which again would aggravate the inflammatory response [235, 236].
11. Why Do Biofilm Infection Occur and Is the Host Defence Indeed a “Mission Impossible”?
Basically, neutrophils have the potential to prevent biofilm formation, recognise, phagocytose, and clear bacterial biofilms nevertheless persistent infections occur. This does not necessarily mean that biofilm formation is never prevented and that biofilms are never eradicated, because an efficient host defence might occur unnoticed, and the frequency of infections, particularly by opportunists, becomes only apparent, when patients with immunodeficiencies are considered. A hint that biofilm infections can be controlled comes from analysing osteosynthesis materials, routinely removed from patients with bone fractures. By advanced techniques, bacteria could be recovered from these materials, despite the fact that the patients showed no sign of infection .
Assuming that neutrophils can clear biofilms the question arises why infections persist. I think the paradigma “too-little-too-late, applies especially well to biofilm infections on implants, because artificial surfaces are prone to be colonised by bacteria. Gristina et al. called that “race for the surface”  and suggested that early colonisation of an appropriate surface would accelerate biofilm formation and that thereby opportunists would acquire virulence factors. Since that time, numerous studies confirmed that artificial surface promotes biofilm formation thereby giving the bacteria a clear advantage over the host defence [238, 239], reviewed in [58, 59], and explains why patients with orthopaedic implants may have a high risk to develop an infection and why in experimentally induced infections less bacteria are required in animals with inlaying metal . The same reasoning applies to patients with infection due to indwelling catheters, because the surface of these devices is also readily colonised by bacteria, infections occur and may spread. Since catheters are used frequently in critically ill patients, an enhanced susceptibility towards infection is also possible [240–243]. In addition to artificial surfaces, also a compromised epithelium could favour biofilm formation, because the initial colonisation by bacteria cannot be prevented. In addition to conditions that favour the adherence of and hence the initial colonisation by bacteria, also predisposing factors of the host have to be considered. Underlying diseases might compromise an effective immune response, for example, diabetes, cancer, or immune-mediated disease, but also exogenous factors like obesity or smoking [244–246]. Aside from these acquired impairments of the immune response also genetically determined “primary” immunodeficiencies have to be considered. According to most textbooks, immunodeficiencies are rare, life-threatening conditions, caused by a gene defect that affects expression of central receptors, enzymes, signalling molecules, or the differentiation of immunocompetent cells. Those defects are usually monogenic and inherited in either x-linked or autosomal manner [247, 248]. In recent years, however, it became increasingly clear, that immunodeficiencies might be not that rare. Probably each individual suffers from some immunodeficiency or other, which might predispose to infection by a single, defined agent in otherwise healthy patients. Because these defects are not necessarily associated with an easy-to-detect phenotype and might not reside in haematopoietic cells, they will escape the routine detection [249–251].
In conclusion, I would say that the defence against biofilms is not a “mission impossible” but that it might occur regularly and very possibly by means of early intervention. Only when the bacteria get a “head-start” and win the “race for the surface,” biofilms may form and bacteria may escape eradication; when the immune cells are abundant and early enough biofilm formation will be controlled mission accomplished.
- J. W. Costerton, “Introduction to biofilm,” International Journal of Antimicrobial Agents, vol. 11, no. 3-4, pp. 217–221, 1999.
- W. Costerton, R. Veeh, M. Shirtliff, M. Pasmore, C. Post, and G. Ehrlich, “The application of biofilm science to the study and control of chronic bacterial infections,” Journal of Clinical Investigation, vol. 112, no. 10, pp. 1466–1477, 2003.
- M. R. Parsek and P. K. Singh, “Bacterial biofilms: an emerging link to disease pathogenesis,” Annual Review of Microbiology, vol. 57, pp. 677–701, 2003.
- L. Hall-Stoodley and P. Stoodley, “Biofilm formation and dispersal and the transmission of human pathogens,” Trends in Microbiology, vol. 13, no. 1, pp. 7–10, 2005.
- A. S. Prince, “Biofilms, antimicrobial resistance, and airway infection,” New England Journal of Medicine, vol. 347, no. 14, pp. 1110–1111, 2002.
- W. J. Looney, M. Narita, and K. Mühlemann, “Stenotrophomonas maltophilia: an emerging opportunist human pathogen,” The Lancet Infectious Diseases, vol. 9, no. 5, pp. 312–323, 2009.
- L. Hall-Stoodley and P. Stoodley, “Evolving concepts in biofilm infections,” Cellular Microbiology, vol. 11, no. 7, pp. 1034–1043, 2009.
- H. C. Flemming, “Biofouling in water systems—cases, causes and countermeasures,” Applied Microbiology and Biotechnology, vol. 59, no. 6, pp. 629–640, 2002.
- W. M. Dunne Jr., “Bacterial adhesion: seen any good biofilms lately?” Clinical Microbiology Reviews, vol. 15, no. 2, pp. 155–166, 2002.
- R. M. Donlan and J. W. Costerton, “Biofilms: survival mechanisms of clinically relevant microorganisms,” Clinical Microbiology Reviews, vol. 15, no. 2, pp. 167–193, 2002.
- L. R. Johnson, “Microcolony and biofilm formation as a survival strategy for bacteria,” Journal of Theoretical Biology, vol. 251, no. 1, pp. 24–34, 2008.
- S. Macfarlane and J. F. Dillon, “Microbial biofilms in the human gastrointestinal tract,” Journal of Applied Microbiology, vol. 102, no. 5, pp. 1187–1196, 2007.
- K. M. Sproule-Willoughby, M. M. Stanton, K. P. Rioux, D. M. McKay, A. G. Buret, and H. Ceri, “In vitro anaerobic biofilms of human colonic microbiota,” Journal of Microbiological Methods, vol. 83, no. 3, pp. 296–301, 2010.
- G. O'Toole, H. B. Kaplan, and R. Kolter, “Biofilm formation as microbial development,” Annual Review of Microbiology, vol. 54, pp. 49–79, 2000.
- L. Hall-Stoodley, J. W. Costerton, and P. Stoodley, “Bacterial biofilms: from the natural environment to infectious diseases,” Nature Reviews Microbiology, vol. 2, no. 2, pp. 95–108, 2004.
- P. Stoodley, K. Sauer, D. G. Davies, and J. W. Costerton, “Biofilms as complex differentiated communities,” Annual Review of Microbiology, vol. 56, pp. 187–209, 2002.
- E. Karatan and P. Watnick, “Signals, regulatory networks, and materials that build and break bacterial biofilms,” Microbiology and Molecular Biology Reviews, vol. 73, no. 2, pp. 310–347, 2009.
- C. Fuqua and E. P. Greenberg, “Listening in on bacteria: acyl-homoserine lactone signalling,” Nature Reviews Molecular Cell Biology, vol. 3, no. 9, pp. 685–695, 2002.
- K. K. Jefferson, “What drives bacteria to produce a biofilm?” FEMS Microbiology Letters, vol. 236, no. 2, pp. 163–173, 2004.
- S. Molin and T. Tolker-Nielsen, “Gene transfer occurs with enhanced efficiency in biofilms and induces enhanced stabilisation of the biofilm structure,” Current Opinion in Biotechnology, vol. 14, no. 3, pp. 255–261, 2003.
- S. Wuertz, S. Okabe, and M. Hausner, “Microbial communities and their interactions in biofilm systems: an overview,” Water Science and Technology, vol. 49, no. 11-12, pp. 327–336, 2004.
- R. M. Donlan, “Role of biofilms antimicrobial resistance,” ASAIO Journal, vol. 46, no. 6, pp. S47–S52, 2000.
- P. S. Stewart and J. W. Costerton, “Antibiotic resistance of bacteria in biofilms,” Lancet, vol. 358, no. 9276, pp. 135–138, 2001.
- M. Whiteley, M. G. Bangera, R. E. Bumgarner et al., “Gene expression in Pseudomonas aeruginosa biofilms,” Nature, vol. 413, no. 6858, pp. 860–864, 2001.
- T. F. C. Mah and G. A. O'Toole, “Mechanisms of biofilm resistance to antimicrobial agents,” Trends in Microbiology, vol. 9, no. 1, pp. 34–39, 2001.
- D. Neut, J. R. Van Horn, T. G. Van Kooten, H. C. Van Der Mei, and H. J. Busscher, “Detection of biomaterial-associated infections in orthopaedic joint implants,” Clinical Orthopaedics and Related Research, no. 413, pp. 261–268, 2003.
- A. Trampuz, D. R. Osmon, A. D. Hanssen, J. M. Steckelberg, and R. Patel, “Molecular and antibiofilm approaches to prosthetic joint infection,” Clinical Orthopaedics and Related Research, no. 414, pp. 69–88, 2003.
- C. L. Nelson, A. C. McLaren, S. G. McLaren, J. W. Johnson, and M. S. Smeltzer, “Is aseptic loosening truly aseptic?” Clinical Orthopaedics and Related Research, no. 437, pp. 25–30, 2005.
- J. B. Lyczak, C. L. Cannon, and G. B. Pier, “Establishment of Pseudomonas aeruginosa infection: lessons from a versatile opportunist,” Microbes and Infection, vol. 2, no. 9, pp. 1051–1060, 2000.
- K. G. Kerr and A. M. Snelling, “Pseudomonas aeruginosa: a formidable and ever-present adversary,” Journal of Hospital Infection, vol. 73, no. 4, pp. 338–344, 2009.
- N. Hoiby, E. W. Flensborg, B. Beck, et al., “Pseudomonas aeruginosa infection in cystic fibrosis. Diagnostic and prognostic significance of Pseudomonas aeruginosa precipitins determined by means of crossed immunoelectrophoresis,” Scandinavian Journal of Respiratory Diseases, vol. 58, pp. 65–79, 1977.
- J. R. W. Govan and V. Deretic, “Microbial pathogenesis in cystic fibrosis: mucoid Pseudomonas aeruginosa and Burkholderia cepacia,” Microbiological Reviews, vol. 60, no. 3, pp. 539–574, 1996.
- D. G. Downey, S. C. Bell, and J. S. Elborn, “Neutrophils in cystic fibrosis,” Thorax, vol. 64, no. 1, pp. 81–88, 2009.
- J. W. Costerton, “Cystic fibrosis pathogenesis and the role of biofilms in persistent infection,” Trends in Microbiology, vol. 9, no. 2, pp. 50–52, 2001.
- G. B. Pier, “Role of the cystic fibrosis transmembrane conductance regulator in innate immunity to Pseudomonas aeruginosa infections,” Proceedings of the National Academy of Sciences of the United States of America, vol. 97, no. 16, pp. 8822–8828, 2000.
- T. Bjarnsholt, K. Kirketerp-Møller, P. Ø. Jensen et al., “Why chronic wounds will not heal: a novel hypothesis,” Wound Repair and Regeneration, vol. 16, no. 1, pp. 2–10, 2008.
- G. A. James, E. Swogger, R. Wolcott et al., “Biofilms in chronic wounds,” Wound Repair and Regeneration, vol. 16, no. 1, pp. 37–44, 2008.
- L. Hall-Stoodley, F. Z. Hu, A. Gieseke et al., “Direct detection of bacterial biofilms on the middle-ear mucosa of children with chronic otitis media,” Journal of the American Medical Association, vol. 296, no. 2, pp. 202–211, 2006.
- C. Chen, “Periodontitis as a biofilm infection,” Journal of the California Dental Association, vol. 29, no. 5, pp. 362–369, 2001.
- C. Schaudinn, A. Gorur, D. Keller, P. P. Sedghizadeh, and J. W. Costerton, “Periodontitis: an archetypical biofilm disease,” Journal of the American Dental Association, vol. 140, no. 8, pp. 978–986, 2009.
- J. Cryer, I. Schipor, J. R. Perloff, and J. N. Palmer, “Evidence of bacterial biofilms in human chronic sinusitis,” Journal for Oto-Rhino-Laryngology, vol. 66, no. 3, pp. 155–158, 2004.
- C. N. Burkhart and C. G. Burkhart, “Microbiology's principle of biofilms as a major factor in the pathogenesis of acne vulgaris,” International Journal of Dermatology, vol. 42, no. 12, pp. 925–927, 2003.
- T. Coenye, K. Honraet, B. Rossel, and H. J. Nelis, “Biofilms in skin infections: propionibacterium acnes and acne vulgaris,” Infectious Disorders, vol. 8, no. 3, pp. 156–159, 2008.
- S. E. Dowd, R. D. Wolcott, Y. Sun, T. McKeehan, E. Smith, and D. Rhoads, “Polymicrobial nature of chronic diabetic foot ulcer biofilm infections determined using bacterial tag encoded FLX amplicon pyrosequencing (bTEFAP),” PLoS ONE, vol. 3, no. 10, Article ID e3326, 2008.
- A. S. Lynch and G. T. Robertson, “Bacterial and fungal biofilm infections,” Annual Review of Medicine, vol. 59, pp. 415–428, 2008.
- T. Tolker-Nielsen, U. C. Brinch, P. C. Ragas, J. B. Andersen, C. S. Jacobsen, and S. Molin, “Development and dynamics of Pseudomonas sp. biofilms,” Journal of Bacteriology, vol. 182, no. 22, pp. 6482–6489, 2000.
- M. Harmsen, L. Yang, S. J. Pamp, and T. Tolker-Nielsen, “An update on Pseudomonas aeruginosa biofilm formation, tolerance, and dispersal,” FEMS Immunology and Medical Microbiology, vol. 59, no. 3, pp. 253–268, 2010.
- C. Wagner, S. Aytac, and G. M. Hansch, “Biofilm growth on implants: bacteria prefer plasma coats,” International Journal of Artificial Organs, vol. 34, pp. 811–817, 2011.
- A. G. Gristina, P. Naylor, and Q. Myrvik, “Infections from biomaterials and implants: a race for the surface,” Medical Progress through Technology, vol. 14, no. 3-4, pp. 205–224, 1988.
- C. K. Chun, E. A. Ozer, M. J. Welsh, J. Zabner, and E. P. Greenberg, “Inactivation of a Pseudomonas aeruginosa quorum-sensing signal by human airway epithelia,” Proceedings of the National Academy of Sciences of the United States of America, vol. 101, no. 10, pp. 3587–3590, 2004.
- J. W. Hastings, “Bacterial quorum-sensing signals are inactivated by mammalian cells,” Proceedings of the National Academy of Sciences of the United States of America, vol. 101, no. 12, pp. 3993–3994, 2004.
- N. Høiby, “Inflammation and infection in cystic fibrosis—hen or egg?” European Respiratory Journal, vol. 17, no. 1, pp. 4–5, 2001.
- P. B. Davis, “Cystic fibrosis since 1938,” American Journal of Respiratory and Critical Care Medicine, vol. 173, no. 5, pp. 475–482, 2006.
- G. B. Pier, “The challenges and promises of new therapies for cystic fibrosis,” The Journal of Experimental Medicine, vol. 209, pp. 1235–1239, 2012.
- S. S. Pedersen, N. Hoiby, F. Espersen, and C. Koch, “Role of alginate in infection with mucoid Pseudomonas aeruginosa in cystic fibrosis,” Thorax, vol. 47, no. 1, pp. 6–13, 1992.
- D. P. Lew and F. A. Waldvogel, “Current concepts: osteomyelitis,” New England Journal of Medicine, vol. 336, no. 14, pp. 999–1007, 1997.
- W. Zimmerli, A. Trampuz, and P. E. Ochsner, “Current concepts: prosthetic-joint infections,” New England Journal of Medicine, vol. 351, no. 16, pp. 1645–1654, 2004.
- J. W. Costerton, L. Montanaro, and C. R. Arciola, “Biofilm in implant infections: its production and regulation,” International Journal of Artificial Organs, vol. 28, no. 11, pp. 1062–1068, 2005.
- C. A. Fux, J. W. Costerton, P. S. Stewart, and P. Stoodley, “Survival strategies of infectious biofilms,” Trends in Microbiology, vol. 13, no. 1, pp. 34–40, 2005.
- L. G. Harris and R. G. Richards, “Staphylococci and implant surfaces: a review,” Injury, vol. 37, no. 2, pp. S3–S14, 2006.
- L. A. Poultsides, L. L. Liaropoulus, and K. N. Malizos, “The socioeconomic Impact of Musculoskeletal Infections,” The Journal of Bone & Joint Surgery, vol. 92, no. 11, pp. 1–12, 2010.
- C. R. Arciola, “Why focus on implant infections?” International Journal of Artificial Organs, vol. 28, no. 11, pp. 1060–1061, 2005.
- C. Wagner, K. Kondella, T. Bernschneider, V. Heppert, A. Wentzensen, and G. M. Hänsch, “Post-traumatic osteomyelitis: analysis of inflammatory cells recruited into the site of infection,” Shock, vol. 20, no. 6, pp. 503–510, 2003.
- M. M. Gaida, F. Günther, C. Wagner et al., “Expression of the CXCR6 on polymorphonuclear neutrophils in pancreatic carcinoma and in acute, localized bacterial infections,” Clinical and Experimental Immunology, vol. 154, no. 2, pp. 216–223, 2008.
- C. Wagner, A. Kaksa, W. Müller et al., “Polymorphonuclear neutrophils in posttraumatic osteomyelitis: cells recovered from the inflamed site lack chemotactic activity but generate superoxides,” Shock, vol. 22, no. 2, pp. 108–115, 2004.
- C. Wagner, D. Heck, K. Lautenschläger et al., “T lymphocytes in implant-associated posttraumatic osteomyelitis: identification of cytotoxic T effector cells at the site of infection,” Shock, vol. 25, no. 3, pp. 241–246, 2006.
- D. Kotsougiani, M. Pioch, B. Prior, V. Heppert, G. M. Hansch, and C. Wagner, “Activation of T lymphocytes in response to persistent bacterial infection: induction of CD11b and of toll-like receptors on T cells,” International Journal of Inflammation, vol. 2010, Article ID 526740, 10 pages, 2010.
- M. M. Gaida, B. Mayer, S. Stegmaier, P. Schirmacher, C. Wagner, and G.M. Hänsch, “Polymorphonuclear neutrophils in osteomyelitis: link to osteoclast generation and bone resorption,” European Journal of Inflammation. In press.
- H. Tlaskalova-Hogenova, R. Stepankova, T. Hudcovic, et al., “Commensal bacteria (normal microflora), mucosal immunity and chronic inflammatory and autoimmune diseases,” Immunology Letters, vol. 93, pp. 97–108, 2004.
- A. J. Macpherson and N. L. Harris, “Interactions between commensal intestinal bacteria and the immune system,” Nature Reviews Immunology, vol. 4, no. 6, pp. 478–485, 2004.
- D. Kelly, S. Conway, and R. Aminov, “Commensal gut bacteria: mechanisms of immune modulation,” Trends in Immunology, vol. 26, no. 6, pp. 326–333, 2005.
- S. L. Russell, M. J. Gold, and M. Hartmann, “Early life antibiotic-driven changes in microbiota enhance susceptibility to allergic asthma,” EMBO Reports, vol. 13, pp. 440–447, 2012.
- D. M. Underhill and A. Ozinsky, “Phagocytosis of microbes: complexity in action,” Annual Review of Immunology, vol. 20, pp. 825–852, 2002.
- L. M. Stuart and R. A. B. Ezekowitz, “Phagocytosis: elegant complexity,” Immunity, vol. 22, no. 5, pp. 539–550, 2005.
- B. Fournier and D. J. Philpott, “Recognition of Staphylococcus aureus by the innate immune system,” Clinical Microbiology Reviews, vol. 18, no. 3, pp. 521–540, 2005.
- M. C. Dinauer, “Disorders of neutrophil function: an overview,” Methods in Molecular Biology, vol. 412, pp. 489–504, 2007.
- N. Berliner, M. Horwitz, and T. P. Loughran, “Congenital and acquired neutropenia,” Hematology, pp. 63–79, 2004.
- L. Notarangelo, J. L. Casanova, A. Fischer et al., “Primary immunodeficiency diseases: an update,” Journal of Allergy and Clinical Immunology, vol. 114, no. 3, pp. 677–687, 2004.
- P. Friedl and B. Weigelin, “Interstitial leukocyte migration and immune function,” Nature Immunology, vol. 9, no. 9, pp. 960–969, 2008.
- C. H. Y. Wong, B. Heit, and P. Kubes, “Molecular regulators of leucocyte chemotaxis during inflammation,” Cardiovascular Research, vol. 86, no. 2, pp. 183–191, 2010.
- V. Witko-Sarsat, P. Rieu, B. Descamps-Latscha, P. Lesavre, and L. Halbwachs-Mecarelli, “Neutrophils: molecules, functions and pathophysiological aspects,” Laboratory Investigation, vol. 80, no. 5, pp. 617–654, 2000.
- D. Rossi and A. Zlotnik, “The biology of chemokines and their receptors,” Annual Review of Immunology, vol. 18, pp. 217–243, 2000.
- C. Gerard and N. P. Gerard, “Chemokines: back to the future?” Nature Cell Biology, vol. 3, no. 2, pp. E53–E54, 2001.
- Y. Kobayashi, “The role of chemokines in neutrophil biology,” Frontiers in Bioscience, vol. 13, no. 7, pp. 2400–2407, 2008.
- E. Schiffmann, H. V. Showell, and B. A. Corcoran, “The isolation and partial characterization of neutrophil chemotactic factors from Escherichia coli,” Journal of Immunology, vol. 114, no. 6, pp. 1831–1837, 1975.
- Y. Miyake, T. Yasuhara, and K. Fukui, “Purification and characterization of neutrophil chemotactic factors of Streptococcus sanguis,” Biochimica et Biophysica Acta, vol. 758, no. 2, pp. 181–186, 1983.
- W. A. Marasco, S. H. Phan, and H. Krutzsch, “Purification and identification of formyl-methionyl-leucyl-phenylalanine as the major peptide neutrophil chemotactic factor produced by Escherichia coli,” Journal of Biological Chemistry, vol. 259, no. 9, pp. 5430–5439, 1984.
- S. Zimmermann, C. Wagner, W. Müller et al., “Induction of neutrophil chemotaxis by the quorum-sensing molecule N-(3-oxododecanoyl)-L-homoserine lactone,” Infection and Immunity, vol. 74, no. 10, pp. 5687–5692, 2006.
- N. A. Kahle, G. Brenner-Weiss, J. Overhage, U. Obst, and G. M. Hansch, “Bacterial quorum sensing molecule induces chemotaxis of human neutrophils via induction of p38 and leukocyte specific protein 1 (LSP1),” Immunobiology. In press.
- E. Vikström, K. E. Magnusson, and A. Pivoriunas, “The Pseudomonas aeruginosa quorum-sensing molecule N-(3-oxododecanoyl)-L- homoserine lactone stimulates phagocytic activity in human macrophages through the p38 MAPK pathway,” Microbes and Infection, vol. 7, no. 15, pp. 1512–1518, 2005.
- T. Karlsson, F. Musse, K. E. Magnusson, and E. Vikstrom, “N-Acylhomoserine lactones are potent neutrophil chemoattractants that act via calcium mobilization and actin remodeling,” Journal of Leukocyte Biology, vol. 91, pp. 15–26, 2012.
- H. M. Chapel, R. Geha, and F. Rosen, “Primary immunodeficiency diseases: an update,” Clinical and Experimental Immunology, vol. 132, no. 1, pp. 9–15, 2003.
- J. A. Lekstrom-Himes and J. I. Gallin, “Immunodeficiency diseases caused by defects in phagocytes,” New England Journal of Medicine, vol. 343, no. 23, pp. 1703–1714, 2000.
- N. Borregaard, “Neutrophils, from Marrow to microbes,” Immunity, vol. 33, no. 5, pp. 657–670, 2010.
- M. Häger, J. B. Cowland, and N. Borregaard, “Neutrophil granules in health and disease,” Journal of Internal Medicine, vol. 268, no. 1, pp. 25–34, 2010.
- E. Meyle, P. Stroh, F. Günther, T. Hoppy-Tichy, C. Wagner, and G. M. Hänsch, “Destruction of bacterial biofilms by polymorphonuclear neutrophils: relative contribution of phagocytosis, DNA release, and degranulation,” International Journal of Artificial Organs, vol. 33, no. 9, pp. 608–620, 2010.
- P. K. Singh, M. R. Parsek, E. P. Greenberg, and M. J. Welsh, “A component of innate immunity prevents bacterial biofilm development,” Nature, vol. 417, no. 6888, pp. 552–555, 2002.
- T. Ganz, “Defensins: antimicrobial peptides of innate immunity,” Nature Reviews Immunology, vol. 3, no. 9, pp. 710–720, 2003.
- K. L. Brown and R. E. W. Hancock, “Cationic host defense (antimicrobial) peptides,” Current Opinion in Immunology, vol. 18, no. 1, pp. 24–30, 2006.
- A. Peschel, “How do bacteria resist human antimicrobial peptides?” Trends in Microbiology, vol. 10, no. 4, pp. 179–186, 2002.
- A. Ozinsky, D. M. Underhill, J. D. Fontenot et al., “The repertoire for pattern recognition of pathogens by the innate immune system is defined by cooperation between Toll-like receptors,” Proceedings of the National Academy of Sciences of the United States of America, vol. 97, no. 25, pp. 13766–13771, 2000.
- R. Medzhitov and C. A. Janeway Jr., “Decoding the patterns of self and nonself by the innate immune system,” Science, vol. 296, no. 5566, pp. 298–300, 2002.
- S. Akira and H. Hemmi, “Recognition of pathogen-associated molecular patterns by TLR family,” Immunology Letters, vol. 85, no. 2, pp. 85–95, 2003.
- J. A. Hoffmann, F. C. Kafatos, C. A. Janeway, and R. A. B. Ezekowitz, “Phylogenetic perspectives in innate immunity,” Science, vol. 284, no. 5418, pp. 1313–1318, 1999.
- T. Nürnberger and F. Brunner, “Innate immunity in plants and animals: emerging parallels between the recognition of general elicitors and pathogen-associated molecular patterns,” Current Opinion in Plant Biology, vol. 5, no. 4, pp. 318–324, 2002.
- S. D. Wright, R. A. Ramos, A. Hermanowski-Vosatka, P. Rockwell, and P. A. Detmers, “Activation of the adhesive capacity of CR3 on neutrophils by endotoxin: dependence on lipopolysaccharide binding protein and CD14,” Journal of Experimental Medicine, vol. 173, no. 5, pp. 1281–1286, 1991.
- M. Triantafilou and K. Triantafilou, “Lipopolysaccharide recognition: CD14, TLRs and the LPS-activation cluster,” Trends in Immunology, vol. 23, no. 6, pp. 301–304, 2002.
- P. J. Gough and S. Gordon, “The role of scavenger receptors in the innate immune system,” Microbes and Infection, vol. 2, no. 3, pp. 305–311, 2000.
- T. Areschoug and S. Gordon, “Scavenger receptors: role in innate immunity and microbial pathogenesis,” Cellular Microbiology, vol. 11, no. 8, pp. 1160–1169, 2009.
- C. B. Whitchurch, T. Tolker-Nielsen, P. C. Ragas, and J. S. Mattick, “Extracellular DNA required for bacterial biofilm formation,” Science, vol. 295, no. 5559, p. 1487, 2002.
- K. C. Rice, E. E. Mann, J. L. Endres et al., “The cidA murein hydrolase regulator contributes to DNA release and biofilm development in Staphylococcus aureus,” Proceedings of the National Academy of Sciences of the United States of America, vol. 104, no. 19, pp. 8113–8118, 2007.
- A. L. Spoering and M. S. Gilmore, “Quorum sensing and DNA release in bacterial biofilms,” Current Opinion in Microbiology, vol. 9, no. 2, pp. 133–137, 2006.
- H. Wagner, “The immunobiology of the TLR9 subfamily,” Trends in Immunology, vol. 25, no. 7, pp. 381–386, 2004.
- A. S. Trevani, A. Chorny, G. Salamone et al., “Bacterial DNA activates human neutrophils by a CpG-independent pathway,” European Journal of Immunology, vol. 33, no. 11, pp. 3164–3174, 2003.
- M. E. Alvarez, J. I. F. Bass, J. R. Geffner et al., “Neutrophil signaling pathways activated by bacterial DNA stimulation,” Journal of Immunology, vol. 177, no. 6, pp. 4037–4046, 2006.
- D. El Kebir, L. József, and J. G. Filep, “Neutrophil recognition of bacterial DNA and Toll-like receptor 9-dependent and -independent regulation of neutrophil function,” Archivum Immunologiae et Therapiae Experimentalis, vol. 56, no. 1, pp. 41–53, 2008.
- K. J. Ishii, S. Koyama, A. Nakagawa, C. Coban, and S. Akira, “Host innate immune receptors and beyond: making sense of microbial infections,” Cell Host and Microbe, vol. 3, no. 6, pp. 352–363, 2008.
- J. Verhoef, P. K. Peterson, and Y. Kim, “Opsonic requirements for staphylococcal phagocytosis. Heterogeneity among strains,” Immunology, vol. 33, no. 2, pp. 191–197, 1977.
- M. M. Frank and L. F. Fries, “The role of complement in inflammation and phagocytosis,” Immunology Today, vol. 12, no. 9, pp. 322–326, 1991.
- K. M. Cunnion and M. M. Frank, “Complement activation influences Staphylococcus aureus adherence to endothelial cells,” Infection and Immunity, vol. 71, no. 3, pp. 1321–1327, 2003.
- E. J. Brown, “Complement receptors and phagocytosis,” Current Opinion in Immunology, vol. 3, pp. 76–82, 1991.
- J. V. Ravetch and R. A. Clynes, “Divergent roles for Fc receptors and complement in vivo,” Annual Review of Immunology, vol. 16, pp. 421–432, 1998.
- J. V. Ravetch and S. Bolland, “IgG Fc receptors,” Annual Review of Immunology, vol. 19, pp. 275–290, 2001.
- S. Rivas-Fuentes, E. García-García, G. Nieto-Castañeda, and C. Rosales, “Fcγ receptors exhibit different phagocytosis potential in human neutrophils,” Cellular Immunology, vol. 263, no. 1, pp. 114–121, 2010.
- D. M. Underhill and H. S. Goodridge, “Information processing during phagocytosis,” Nature Reviews Immunology, vol. 12, pp. 492–502, 2012.
- D. C. Hodgins and P. E. Shewen, “Subversion of the immune response by bacterial pathogens,” in Pathogenesis of Bacterial Infections in Animals, pp. 15–32, Wiley-Blackwell, 2010.
- F. R. DeLeo, B. A. Diep, and M. Otto, “Host defense and pathogenesis in Staphylococcus aureus infections,” Infectious Disease Clinics of North America, vol. 23, no. 1, pp. 17–34, 2009.
- T. J. Foster, “Colonization and infection of the human host by staphylococci: adhesion, survival and immune evasion,” Veterinary Dermatology, vol. 20, no. 5-6, pp. 456–470, 2009.
- D. M. Veltman, I. Keizer-Gunnik, and P. J. M. Van Haastert, “Four key signaling pathways mediating chemotaxis in Dictyostelium discoideum,” Journal of Cell Biology, vol. 180, no. 4, pp. 747–753, 2008.
- A. Bagorda and C. A. Parent, “Eukaryotic chemotaxis at a glance,” Journal of Cell Science, vol. 121, no. 16, pp. 2621–2624, 2008.
- J. S. King and R. H. Insall, “Chemotaxis: finding the way forward with Dictyostelium,” Trends in Cell Biology, vol. 19, no. 10, pp. 523–530, 2009.
- S. S. Branda, S. Vik, L. Friedman, and R. Kolter, “Biofilms: the matrix revisited,” Trends in Microbiology, vol. 13, no. 1, pp. 20–26, 2005.
- I. W. Sutherland, “The biofilm matrix—an immobilized but dynamic microbial environment,” Trends in Microbiology, vol. 9, no. 5, pp. 222–227, 2001.
- H. C. Flemming and J. Wingender, “The biofilm matrix,” Nature Reviews Microbiology, vol. 8, no. 9, pp. 623–633, 2010.
- A. J. Jesaitis, M. J. Franklin, D. Berglund et al., “Compromised host defense on Pseudomonas aeruginosa biofilms: characterization of neutrophil and biofilm interactions,” Journal of Immunology, vol. 171, no. 8, pp. 4329–4339, 2003.
- E. Tvenstrup Jensen, A. Kharazmi, N. Hoiby, and J. W. Costeron, “Some bacterial parameters influencing the neutrophil oxidative burst response to Pseudomonas aeruginosa biofilms,” Acta Pathologica, Microbiologica et Immunologica, vol. 100, no. 8, pp. 727–733, 1992.
- A. Kharazmi, “Mechanisms involved in the evasion of the host defence by Pseudomonas aeruginosa,” Immunology Letters, vol. 30, no. 2, pp. 201–206, 1991.
- A. Kharazmi and H. Nielsen, “Inhibition of human monocyte chemotaxis and chemiluminescence by Pseudomonas aeruginosa elastase,” Acta Pathologica, Microbiologica et Immunologica, vol. 99, no. 1, pp. 93–95, 1991.
- J. G. Leid, C. J. Willson, M. E. Shirtliff, D. J. Hassett, M. R. Parsek, and A. K. Jeffers, “The exopolysaccharide alginate protects Pseudomonas aeruginosa biofilm bacteria from IFN-γ-mediated macrophage killing,” Journal of Immunology, vol. 175, no. 11, pp. 7512–7518, 2005.
- G. M. Hänsch, G. Brenner-Weiss, B. Prior, C. Wagner, and U. Obst, “The extracellular matrix of Pseudomonas aeruginosa: too slippery to migrate on?” International Journal of Artificial Organs, vol. 31, pp. 796–803, 2008.
- D. W. Martin, M. J. Schurr, M. H. Mudd, J. R. W. Govan, B. W. Holloway, and V. Deretic, “Mechanism of conversion to mucoidy in Pseudomonas aeruginosa infecting cystic fibrosis patients,” Proceedings of the National Academy of Sciences of the United States of America, vol. 90, no. 18, pp. 8377–8381, 1993.
- M. Hentzer, G. M. Teitzel, G. J. Balzer et al., “Alginate overproduction affects pseudomonas aeruginosa biofilm structure and function,” Journal of Bacteriology, vol. 183, no. 18, pp. 5395–5401, 2001.
- F. G. Jarvis and M. J. Johnson, “A glyco-lipide produced by Pseudomonas Aeruginosa,” The Journal of the American Chemical Society, vol. 71, no. 12, pp. 4124–4126, 1949.
- U. A. Ochsner, J. Reiser, A. Fiechter, and B. Witholt, “Production of Pseudomonas aeruginosa rhamnolipid biosurfactants in heterologous hosts,” Applied and Environmental Microbiology, vol. 61, no. 9, pp. 3503–3506, 1995.
- J. P. Pearson, E. C. Pesci, and B. H. Iglewski, “Roles of Pseudomonas aeruginosa las and rhl quorum-sensing systems in control of elastase and rhamnolipid biosynthesis genes,” Journal of Bacteriology, vol. 179, no. 18, pp. 5756–5767, 1997.
- M. E. Davey, N. C. Caiazza, and G. A. O'Toole, “Rhamnolipid surfactant production affects biofilm architecture in Pseudomonas aeruginosa PAO1,” Journal of Bacteriology, vol. 185, no. 3, pp. 1027–1036, 2003.
- A. Kharazmi, Z. Bibi, H. Nielsen, N. Hoiby, and G. Doring, “Effect of Pseudomonas aeruginosa rhamnolipid on human neutrophil and monocyte function,” Acta Pathologica, Microbiologica et Immunologica, vol. 97, no. 12, pp. 1068–1072, 1989.
- T. R. Shryock, S. A. Silver, M. W. Banschbach, and J. C. Kramer, “Effect of Pseudomonas aeruginosa rhamnolipid on human neutrophil migration,” Current Microbiology, vol. 10, no. 6, pp. 323–328, 1984.
- P. Ø. Jensen, T. Bjarnsholt, R. Phipps et al., “Rapid necrotic killing of polymorphonuclear leukocytes is caused by quorum-sensing-controlled production of rhamnolipid by Pseudomonas aeruginosa,” Microbiology, vol. 153, no. 5, pp. 1329–1338, 2007.
- P. O. Jensen, M. Givskov, T. Bjarnsholt, and C. Moser, “The immune system vs. Pseudomonas aeruginosa biofilms,” FEMS Immunology and Medical Microbiology, vol. 59, no. 3, pp. 292–305, 2010.
- M. van Gennip, L. D. Christensen, M. Alhede et al., “Interactions between polymorphonuclear leukocytes and Pseudomonas aeruginosa biofilms on silicone implants in vivo,” Infection and Immunity, vol. 80, pp. 2601–2607, 2012.
- K. C. Meyer and J. Zimmerman, “Neutrophil mediators, Pseudomonas, and pulmonary dysfunction in cystic fibrosis,” Journal of Laboratory and Clinical Medicine, vol. 121, no. 5, pp. 654–661, 1993.
- J. B. Lyczak, C. L. Cannon, and G. B. Pier, “Lung infections associated with cystic fibrosis,” Clinical Microbiology Reviews, vol. 15, no. 2, pp. 194–222, 2002.
- M. Conese, E. Copreni, S. Di Gioia, P. De Rinaldis, and R. Fumarulo, “Neutrophil recruitment and airway epithelial cell involvement in chronic cystic fibrosis lung disease,” Journal of Cystic Fibrosis, vol. 2, no. 3, pp. 129–135, 2003.
- A. P. Watt, J. Courtney, J. Moore, M. Ennis, and J. S. Elborn, “Neutrophil cell death, activation and bacterial infection in cystic fibrosis,” Thorax, vol. 60, no. 8, pp. 659–664, 2005.
- M. W. Konstan, K. A. Hilliard, T. M. Norvell, and M. Berger, “Bronchoalveolar lavage findings in cystic fibrosis patients with stable, clinically mild lung disease suggest ongoing infection and inflammation,” American Journal of Respiratory and Critical Care Medicine, vol. 150, no. 2, pp. 448–454, 1994.
- K. C. Meyer, J. R. Lewandoski, J. J. Zimmerman, D. Nunley, W. J. Calhoun, and G. A. Dopico, “Human neutrophil elastase and elastase/alpha1-antiprotease complex in cystic fibrosis: comparison with interstitial lung disease and evaluation of the effect of intravenously administered antibiotic therapy,” American Review of Respiratory Disease, vol. 144, no. 3 I, pp. 580–585, 1991.
- M. Alhede, T. Bjarnsholt, P. Ø. Jensen et al., “Pseudomonas aeruginosa recognizes and responds aggressively to the presence of polymorphonuclear leukocytes,” Microbiology, vol. 155, no. 11, pp. 3500–3508, 2009.
- G. Luo, D. W. Niesel, R. A. Shaban, E. A. Grimm, and G. R. Klimpel, “Tumor necrosis factor alpha binding to bacteria: evidence for a high-affinity receptor and alteration of bacterial virulence properties,” Infection and Immunity, vol. 61, no. 3, pp. 830–835, 1993.
- G. Umberto Meduri, S. Kanangat, J. Stefan, E. Tolley, and D. Schaberg, “Cytokines IL-1β, IL-6, and TNF-α enhance in vitro growth of bacteria,” American Journal of Respiratory and Critical Care Medicine, vol. 160, no. 3, pp. 961–967, 1999.
- S. Kanangat, M. S. Bronze, G. Umberto Meduri et al., “Enhanced extracellular growth of Staphylococcus aureus in the presence of selected linear peptide fragments of human interleukin (IL)-1β and IL-1 receptor antagonist,” Journal of Infectious Diseases, vol. 183, no. 1, pp. 65–69, 2001.
- L. Wu, O. Estrada, O. Zaborina et al., “Microbiology: recognition of host immune activation by Pseudomonas aeruginosa,” Science, vol. 309, no. 5735, pp. 774–777, 2005.
- E. Banin, M. L. Vasil, and E. P. Greenberg, “Iron and Pseudomonas aeruginosa biofilm formation,” Proceedings of the National Academy of Sciences of the United States of America, vol. 102, no. 31, pp. 11076–11081, 2005.
- C. Y. O'May, K. Sanderson, L. F. Roddam, S. M. Kirov, and D. W. Reid, “Iron-binding compounds impair Pseudomonas aeruginosa biofilm formation, especially under anaerobic conditions,” Journal of Medical Microbiology, vol. 58, no. 6, pp. 765–773, 2009.
- A. J. Psaltis, P. J. Wormald, K. R. Ha, and L. W. Tan, “Reduced levels of lactoferrin in biofilm-associated chronic rhinosinusitis,” Laryngoscope, vol. 118, no. 5, pp. 895–901, 2008.
- B. E. Britigan, M. B. Hayek, B. N. Doebbeling, and R. B. Fick Jr., “Transferrin and lactoferrin undergo proteolytic cleavage in the Pseudomonas aeruginosa-infected lungs of patients with cystic fibrosis,” Infection and Immunity, vol. 61, no. 12, pp. 5049–5055, 1993.
- M. P. Rogan, C. C. Taggart, C. M. Greene, P. G. Murphy, S. J. O'Neill, and N. G. McElvaney, “Loss of microbial activity and increased formation of biofilm due to decreased lactoferrin activity in patients with cystic fibrosis,” Journal of Infectious Diseases, vol. 190, no. 7, pp. 1245–1253, 2004.
- P. Geraghty, M. P. Rogan, C. M. Greene et al., “Neutrophil elastase up-regulates cathepsin B and matrix metalloprotease-2 expression,” Journal of Immunology, vol. 178, no. 9, pp. 5871–5878, 2007.
- D. R. Ammons, R. Puttagunta, J. C. Granados, G. de la Garza, G. S. Eyambe, and J. Rampersad, “An exploratory study of methicillin-resistant Staphylococcus aureus and SCCmec elements obtained from a community setting along the Texas border with Mexico,” Current Microbiology, vol. 60, no. 5, pp. 321–326, 2010.
- M. C. B. Ammons, L. S. Ward, and G. A. James, “Anti-biofilm efficacy of a lactoferrin/xylitol wound hydrogel used in combination with silver wound dressings,” International Wound Journal, vol. 8, no. 3, pp. 268–273, 2011.
- R. D. Wolcott and D. D. Rhoads, “A study of biofilm-based wound management in subjects with critical limb ischaemia,” Journal of Wound Care, vol. 17, no. 4, pp. 145–155, 2008.
- S. C. Davis, L. Martinez, and R. Kirsner, “The diabetic foot: the importance of biofilms and wound bed preparation,” Current Diabetes Reports, vol. 6, no. 6, pp. 439–445, 2006.
- K. E. Hill, S. Malic, R. McKee et al., “An in vitro model of chronic wound biofilms to test wound dressings and assess antimicrobial susceptibilities,” Journal of Antimicrobial Chemotherapy, vol. 65, no. 6, pp. 1195–1206, 2010.
- A. Nijnik and R. E. W. Hancock, “The roles of cathelicidin LL-37 in immune defences and novel clinical applications,” Current Opinion in Hematology, vol. 16, no. 1, pp. 41–47, 2009.
- P. Méndez-Samperio, “The human cathelicidin hCAP18/LL-37: a multifunctional peptide involved in mycobacterial infections,” Peptides, vol. 31, no. 9, pp. 1791–1798, 2010.
- J. Overhage, A. Campisano, M. Bains, E. C. W. Torfs, B. H. A. Rehm, and R. E. W. Hancock, “Human host defense peptide LL-37 prevents bacterial biofilm formation,” Infection and Immunity, vol. 76, no. 9, pp. 4176–4182, 2008.
- S. K. Chennupati, A. G. Chiu, E. Tamashiro et al., “Effects of an LL-37-derived antimicrobial peptide in an animal model of biofilm Pseudomonas sinusitis,” American Journal of Rhinology and Allergy, vol. 23, no. 1, pp. 46–51, 2009.
- M. Vaara, “New approaches in peptide antibiotics,” Current Opinion in Pharmacology, vol. 9, no. 5, pp. 571–576, 2009.
- E. Hell, C. G. Giske, A. Nelson, U. Römling, and G. Marchini, “Human cathelicidin peptide LL37 inhibits both attachment capability and biofilm formation of Staphylococcus epidermidis,” Letters in Applied Microbiology, vol. 50, no. 2, pp. 211–215, 2010.
- P. W. Tsai, C. Y. Yang, H. T. Chang, and C. Y. Lan, “Human antimicrobial peptide LL-37 inhibits adhesion of Candida albicans by interacting with yeast cell-wall carbohydrates,” PLoS ONE, vol. 6, no. 3, Article ID e17755, 2011.
- L. S. Amer, B. M. Bishop, and M. L. van Hoek, “Antimicrobial and antibiofilm activity of cathelicidins and short, synthetic peptides against Francisella,” Biochemical and Biophysical Research Communications, vol. 396, no. 2, pp. 246–251, 2010.
- G. Telford, D. Wheeler, P. Williams et al., “The Pseudomonas aeruginosa quorum-sensing signal molecule N-(3- Oxododecanoyl)-L-homoserine lactone has immunomodulatory activity,” Infection and Immunity, vol. 66, no. 1, pp. 36–42, 1998.
- S. R. Chhabra, C. Harty, D. S. W. Hooi et al., “Synthetic analogues of the bacterial signal (quorum sensing) molecule N-(3-oxododecanoyl)-L-homoserine lactone as immune modulators,” Journal of Medicinal Chemistry, vol. 46, no. 1, pp. 97–104, 2003.
- A. J. Ritchie, A. O. W. Yam, K. M. Tanabe, S. A. Rice, and M. A. Cooley, “Modification of in vivo and in vitro T- and B-cell-mediated immune responses by the Pseudomonas aeruginosa quorum-sensing molecule n-(3-oxododecanoyl)-L-homoserine lactone,” Infection and Immunity, vol. 71, no. 8, pp. 4421–4431, 2003.
- K. Tateda, Y. Ishii, M. Horikawa et al., “The Pseudomonas aeruginosa autoinducer N-3-oxododecanoyl homoserine lactone accelerates apoptosis in macrophages and neutrophils,” Infection and Immunity, vol. 71, no. 10, pp. 5785–5793, 2003.
- D. T. Hughes and V. Sperandio, “Inter-kingdom signalling: communication between bacteria and their hosts,” Nature Reviews Microbiology, vol. 6, no. 2, pp. 111–120, 2008.
- M. Cooley, S. R. Chhabra, and P. Williams, “N-Acylhomoserine lactone-mediated quorum sensing: a twist in the tail and a blow for host immunity,” Chemistry and Biology, vol. 15, no. 11, pp. 1141–1147, 2008.
- C. Wagner, S. Zimmermann, G. Brenner-Weiss et al., “The quorum-sensing molecule N-3-oxododecanoyl homoserine lactone (3OC12-HSL) enhances the host defence by activating human polymorphonuclear neutrophils (PMN),” Analytical and Bioanalytical Chemistry, vol. 387, no. 2, pp. 481–487, 2007.
- T. Karlsson, M. V. Turkina, O. Yakmenko, K. E. Magnusson, and E. Vikström, “The Pseudomonas aeruginosa N-Acylhomoserine Lactone Quorum Senisng Molecules Target IQGAG1 and modulate Epithelial Cell migration,” PLOS Pathogen, vol. 8, no. 10, Article ID e1002953, 2012.
- A. Jahoor, R. Patel, A. Bryan et al., “Peroxisome proliferator-activated receptors mediate host cell proinflammatory responses to Pseudomonas aeruginosa autoinducer,” Journal of Bacteriology, vol. 190, no. 13, pp. 4408–4415, 2008.
- A. J. Ritchie, C. Whittall, J. J. Lazenby, S. R. Chhabra, D. I. Pritchard, and M. A. Cooley, “The immunomodulatory Pseudomonas aeruginosa signalling molecule N-(3-oxododecanoyl)-L-homoserine lactone enters mammalian cells in an unregulated fashion,” Immunology and Cell Biology, vol. 85, no. 8, pp. 596–602, 2007.
- V. V. Kravchenko, G. F. Kaufmann, J. C. Mathison et al., “N-(3-oxo-acyl)homoserine lactones signal cell activation through a mechanism distinct from the canonical pathogen-associated molecular pattern recognition receptor pathways,” Journal of Biological Chemistry, vol. 281, no. 39, pp. 28822–28830, 2006.
- G. M. Hansch, “Molecular eavesdropping: phagocytic cells spy on bacterial communication,” Journal of Leukocyte Biology, vol. 91, pp. 3–5, 2012.
- T. J. Foster, “Immune evasion by staphylococci,” Nature Reviews Microbiology, vol. 3, no. 12, pp. 948–958, 2005.
- I. Fedtke, F. Götz, and A. Peschel, “Bacterial evasion of innate host defenses—the Staphylococcus aureus lesson,” International Journal of Medical Microbiology, vol. 294, no. 2-3, pp. 189–194, 2004.
- M. Otto, “Staphylococcal biofilms,” Current Topics in Microbiology and Immunology, vol. 322, pp. 207–228, 2008.
- P. Francois, P. H. Tu Quoc, C. Bisognano et al., “Lack of biofilm contribution to bacterial colonisation in an experimental model of foreign body infection by Staphylococcus aureus and Staphylococcus epidermidis,” FEMS Immunology and Medical Microbiology, vol. 35, no. 2, pp. 135–140, 2003.
- M. A. Deighton, R. Borland, and J. A. Capstick, “Virulence of Staphylococcus epidermidis in a mouse model: significance of extracellular slime,” Epidemiology and Infection, vol. 117, no. 2, pp. 267–280, 1996.
- B. Gallimore, R. F. Gagnon, R. Subang, and G. K. Richards, “Natural history of chronic Staphylococcus epidermidis foreign body infection in a mouse model,” Journal of Infectious Diseases, vol. 164, no. 6, pp. 1220–1223, 1991.
- C. R. Arciola, F. I. Alvi, Y. H. An, D. Campoccia, and L. Montanaro, “Implant infection and infection resistant materials: a mini review,” International Journal of Artificial Organs, vol. 28, no. 11, pp. 1119–1125, 2005.
- L. Montanaro, P. Speziale, D. Campoccia, et al., “Scenery of Staphylococcus implant infections in orthopedics,” Future Microbiology, vol. 6, pp. 1329–1349, 2011.
- D. De Wit, R. Mulla, M. R. Cowie, J. C. Mason, and K. A. Davies, “Vertebral osteomyelitis due to Staphylococcus epidermidis,” British Journal of Rheumatology, vol. 32, no. 4, pp. 339–341, 1993.
- J. O. Galdbart, A. Morvan, N. Desplaces, and N. El Solh, “Phenotypic and genomic variation among Staphylococcus epidermidis strains infecting joint prostheses,” Journal of Clinical Microbiology, vol. 37, no. 5, pp. 1306–1312, 1999.
- P. J. Carek, L. M. Dickerson, and J. L. Sack, “Diagnosis and management of osteomyelitis,” American Family Physician, vol. 63, no. 12, pp. 2413–2420, 2001.
- F. Günther, G. H. Wabnitz, J. W. Costerton, P. Stroh, et al., “Host defence against Staphylococcus aureus biofilm infection: Phagocytosis of biofilms by polymorphonuclear neutrophils (PMN),” Molecular Immunology, vol. 46, no. 8-9, pp. 1805–1818, 2009.
- J. G. Leid, M. E. Shirtliff, J. W. Costerton, and P. Stoodley, “Human leukocytes adhere to, penetrate, and respond to Staphylococcus aureus biofilms,” Infection and Immunity, vol. 70, no. 11, pp. 6339–6345, 2002.
- F. Guenther, P. Stroh, C. Wagner, U. Obst, and G. M. Hänch, “Phagocytosis of staphylococci biofilms by polymorphonuclear neutrophils: S. aureus and S. epidermidis differ with regard to their susceptibility towards the host defense,” International Journal of Artificial Organs, vol. 32, no. 9, pp. 565–573, 2009.
- E. Meyle and G. M. Hänsch, “Bacterial biofilms:the ultimate cause of implant-associated infection,” Giornale Italiano di Ortopedia e Traumatologia, vol. 36, no. 1, pp. s1–s3, 2010.
- P. Stroh, F. Günther, E. Meyle, B. Prior, C. Wagner, and G. M. Hänsch, “Host defence against Staphylococcus aureus biofilms by polymorphonuclear neutrophils: oxygen radical production but not phagocytosis depends on opsonisation with immunoglobulin G,” Immunobiology, vol. 216, no. 3, pp. 351–357, 2011.
- S. A. Kristian, T. A. Birkenstock, U. Sauder, D. Mack, F. Götz, and R. Landmann, “Biofilm formation induces C3a release and protects Staphylococcus epidermidis from IgG and complement deposition and from neutrophil-dependent killing,” Journal of Infectious Diseases, vol. 197, no. 7, pp. 1028–1035, 2008.
- L. R. Thurlow, M. L. Hanke, T. Fritz et al., “Staphylococcus aureus biofilms prevent macrophage phagocytosis and attenuate inflammation in vivo,” Journal of Immunology, vol. 186, no. 11, pp. 6585–6596, 2011.
- E. Meyle, G. Brenner-Weiss, U. Obst, B. Prior, and G. M. Hänsch, “Immune defence against S. epidermidis biofilms: components of the extracellular polymeric substance activate distinct bactericidal mechanisms of phagocytic cells,” International Journal of Artificial Organs. In press.
- M. A. Noble, P. E. Reid, C. M. Park, and V. Y. H. Chan, “Inhibition of human neutrophil bacteriocidal activity by extracellular substance from slime-producing Staphylococcus epidermidis,” Diagnostic Microbiology and Infectious Disease, vol. 4, no. 4, pp. 335–339, 1986.
- G. M. Johnson, D. A. Lee, and W. E. Regelmann, “Interference with granulocyte function by Staphylococcus epidermidis slime,” Infection and Immunity, vol. 54, no. 1, pp. 13–20, 1986.
- Q. N. Myrvik, W. Wagner, E. Barth, P. Wood, and A. G. Gristina, “Effects of extracellular slime produced by Staphylococcus epidermidis on oxidative responses of rabbit alveolar macrophages,” Journal of Investigative Surgery, vol. 2, no. 4, pp. 381–389, 1989.
- J. Rodgers, F. Phillips, and C. Olliff, “The effects of extracellular slime from Staphylococcus epidermidis on phagocytic ingestion and killing,” FEMS Immunology and Medical Microbiology, vol. 9, no. 2, pp. 109–115, 1994.
- C. Vuong, S. Kocianova, J. M. Voyich et al., “A crucial role for exopolysaccharide modification in bacterial biofilm formation, immune evasion, and virulence,” Journal of Biological Chemistry, vol. 279, no. 52, pp. 54881–54886, 2004.
- M. E. Rupp, J. S. Ulphani, P. D. Fey, and D. Mack, “Characterization of Staphylococcus epidermidis polysaccharide intercellular adhesin/hemagglutinin in the pathogenesis of intravascular catheter-associated infection in a rat model,” Infection and Immunity, vol. 67, no. 5, pp. 2656–2659, 1999.
- R. Rupp and D. Boichard, “Genetic parameters for clinical mastitis, somatic cell score, production, udder type traits, and milking ease in first lactation Holsteins,” Journal of Dairy Science, vol. 82, no. 10, pp. 2198–2204, 1999.
- J. O. Galdbart, J. Allignet, H. S. Tung, R. Cécilia, and N. El Solh, “Screening for Staphylococcus epidermidis markers discriminating between skin-flora strains and those responsible for infections of joint prostheses,” Journal of Infectious Diseases, vol. 182, no. 1, pp. 351–355, 2000.
- E. Barth, Q. M. Myrvik, W. Wagner, and A. G. Gristina, “In vitro and in vivo comparative colonization of Staphylociccus aureus and Staphylococcus epidermidis on orthopedic implants,” Biomaterials, vol. 10, pp. 325–328, 1989.
- M. Otto, R. Süßmuth, G. Jung, and F. Götz, “Structure of the pheromone peptide of the Staphylococcus epidermis agr system,” FEBS Letters, vol. 424, no. 1-2, pp. 89–94, 1998.
- C. Vuong, C. Gerke, G. A. Somerville, E. R. Fischer, and M. Otto, “Quorum-sensing control of biofilm factors in Staphylococcus epidermidis,” Journal of Infectious Diseases, vol. 188, no. 5, pp. 706–718, 2003.
- C. Vuong, M. Dürr, A. B. Carmondy, A. Peschel, S. J. Klebanoff, and M. Otto, “Regulated expression of pathogen-associated molecular pattern molecules in Staphylococcus epidermis: quorum-sensing determines pro-inflammatory capacity and production of phenol-soluble modulins,” Cellular Microbiology, vol. 6, no. 8, pp. 753–759, 2004.
- Y. Yao, C. Vuong, S. Kocianova et al., “Characterization of the Staphylococcus epidermidis accessory-gene regulator response: quorum-sensing regulation of resistance to human innate host defense,” Journal of Infectious Diseases, vol. 193, no. 6, pp. 841–848, 2006.
- I. K. Mullarky, C. Su, N. Frieze, Y. H. Park, and L. M. Sordillo, “Staphylococcus aureus agr genotypes with enterotoxin production capabilities can resist neutrophil bactericidal activity,” Infection and Immunity, vol. 69, no. 1, pp. 45–51, 2001.
- J. A. Smith, “Neutrophils, host defense, and inflammation: a double-edged sword,” Journal of Leukocyte Biology, vol. 56, no. 6, pp. 672–686, 1994.
- G. Doring, “The role of neutrophil elastase in chronic inflammation,” American Journal of Respiratory and Critical Care Medicine, vol. 150, no. 6, pp. S114–S117, 1994.
- C. Wagner, U. Obst, and G. M. Hänsch, “Implant-associated posttraumatic osteomyelitis: collateral damage by local host defense?” International Journal of Artificial Organs, vol. 28, no. 11, pp. 1172–1180, 2005.
- C. R. Arciola, Y. H. An, D. Campoccia, M. E. Donati, and L. Montanaro, “Etiology of implant orthopedic infections: a survey on 1027 clinical isolates,” International Journal of Artificial Organs, vol. 28, no. 11, pp. 1091–1100, 2005.
- C. R. Arciola, “Host defense against implant infection: the ambivalent role of phagocytosis,” International Journal of Artificial Organs, vol. 33, no. 9, pp. 565–567, 2010.
- J. Savill, “Apoptosis in resolution of inflammation,” Journal of Leukocyte Biology, vol. 61, no. 4, pp. 375–380, 1997.
- C. N. Serhan and J. Savill, “Resolution of inflammation: the beginning programs the end,” Nature Immunology, vol. 6, no. 12, pp. 1191–1197, 2005.
- M. Faurschou and N. Borregaard, “Neutrophil granules and secretory vesicles in inflammation,” Microbes and Infection, vol. 5, no. 14, pp. 1317–1327, 2003.
- T. S. Walker, K. L. Tomlin, G. S. Worthen et al., “Enhanced Pseudomonas aeruginosa biofilm development mediated by human neutrophils,” Infection and Immunity, vol. 73, no. 6, pp. 3693–3701, 2005.
- Q. M. Parks, R. L. Young, K. R. Poch, K. C. Malcolm, M. L. Vasil, and J. A. Nick, “Neutrophil enhancement of Pseudomonas aeruginosa biofilm development: human F-actin and DNA as targets for therapy,” Journal of Medical Microbiology, vol. 58, no. 4, pp. 492–502, 2009.
- U. Obst, S.-M. Marten, C. Niessner, E. Hartwig, M. Korsch, and M. Walther, “Diversity of patients microflora on orthopaedic and dental implants,” International Journal of Artificial Organs. In press.
- M. Oga, Y. Sugioka, C. D. Hobgood, A. G. Gristina, and Q. N. Myrvik, “Surgical biomaterials and differential colonization by Staphylococcus epidermidis,” Biomaterials, vol. 9, no. 3, pp. 285–289, 1988.
- J. Cordero, L. Munuera, and M. D. Folgueira, “Influence of metal implants on infection: an experimental study in rabbits,” Journal of Bone and Joint Surgery Series B, vol. 76, no. 5, pp. 717–720, 1994.
- J. C. Pinilla, D. F. Ross, T. Martin, and H. Crump, “Study of the incidence of intravascular catheter infection and associated septicemia in critically ill patients,” Critical Care Medicine, vol. 11, no. 1, pp. 21–25, 1983.
- I. Raad, “Intravascular-catheter-related infections,” Lancet, vol. 351, no. 9106, pp. 893–898, 1998.
- J. A. Crump and P. J. Collignon, “Intravascular catheter-associated infections,” European Journal of Clinical Microbiology and Infectious Diseases, vol. 19, no. 1, pp. 1–8, 2000.
- B. W. Trautner and R. O. Darouiche, “Role of biofilm in catheter-associated urinary tract infection,” American Journal of Infection Control, vol. 32, no. 3, pp. 177–183, 2004.
- N. Safdar, D. M. Kluger, and D. G. Maki, “A review of risk factors for catheter-related bloodstream infection caused by percutaneously inserted, noncuffed central venous catheters: implications for preventive strategies,” Medicine, vol. 81, no. 6, pp. 466–479, 2002.
- W. Zimmerli and P. E. Ochsner, “Management of infection associated with prosthetic joints,” Infection, vol. 31, no. 2, pp. 99–108, 2003.
- J. L. Del Pozo and R. Patel, “Infection associated with prosthetic joints,” New England Journal of Medicine, vol. 361, no. 8, pp. 787–794, 2009.
- F. S. Rosen, M. D. Cooper, and R. J. P. Wedgwood, “Medical progress: the primary immunodeficiencies,” New England Journal of Medicine, vol. 333, no. 7, pp. 431–440, 1995.
- R. S. Geha, L. D. Notarangelo, J. L. Casanova et al., “Primary immunodeficiency diseases: an update from the International Union of Immunological Societies Primary Immunodeficiency Diseases Classification Committee,” The Journal of Allergy and Clinical Immunology, vol. 120, no. 4, pp. 776–794, 2007.
- J. L. Casanova, C. Fieschi, J. Bustamante et al., “From idiopathic infectious diseases to novel primary immunodeficiencies,” Journal of Allergy and Clinical Immunology, vol. 116, no. 2, pp. 426–430, 2005.
- J. L. Casanova and L. Abel, “Primary immunodeficiencies: a field in its infancy,” Science, vol. 317, no. 5838, pp. 617–619, 2007.
- J. L. Casanova and L. Abel, “Human genetics of infectious diseases: a unified theory,” EMBO Journal, vol. 26, no. 4, pp. 915–922, 2007.