The Role of Pathogenic <i>E. coli</i> in Fresh Vegetables: Behavior, Contamination Factors, and Preventive Measures

Luna-Guevara, J. J.; Arenas-Hernandez, M. M. P.; Martínez de la Peña, C.; Silva, Juan L.; Luna-Guevara, M. L.

doi:https://doi.org/10.1155/2019/2894328

International Journal of Microbiology

On this page

Abstract Introduction Conclusion Conflicts of Interest References Copyright Related Articles

Review Article | Open Access

Volume 2019 | Article ID 2894328 | https://doi.org/10.1155/2019/2894328

The Role of Pathogenic E. coli in Fresh Vegetables: Behavior, Contamination Factors, and Preventive Measures

J. J. Luna-Guevara,¹M. M. P. Arenas-Hernandez,²C. Martínez de la Peña,²Juan L. Silva,³and M. L. Luna-Guevara¹

Academic Editor: Karl Drlica

Received28 Aug 2019

Accepted11 Nov 2019

Published26 Nov 2019

Abstract

Many raw vegetables, such as tomato, chili, onion, lettuce, arugula, spinach, and cilantro, are incorporated into fresh dishes including ready-to-eat salads and sauces. The consumption of these foods confers a high nutritional value to the human diet. However, the number of foodborne outbreaks associated with fresh produce has been increasing, with Escherichia coli being the most common pathogen associated with them. In humans, pathogenic E. coli strains cause diarrhea, hemorrhagic colitis, hemolytic uremic syndrome, and other indications. Vegetables can be contaminated with E. coli at any point from pre- to postharvest. This bacterium is able to survive in many environmental conditions due to a variety of mechanisms, such as adhesion to surfaces and internalization in fresh products, thereby limiting the usefulness of conventional processing and chemical sanitizing methods used by the food industry. The aim of this review is to provide a general description of the behavior and importance of pathogenic E. coli in ready-to-eat vegetable dishes. This information can contribute to the development of effective control measures for enhancing food safety.

1. Introduction

The consumption of fresh produce has increased notably in recent years due to multiple contributions of nutrients and functional properties [1, 2]. Over the last 30 years, there has been a 25% increase in the average amount of fresh produce consumed per person in the USA [3]. A diet rich in fruit and vegetables has been shown to protect against various types of cancer and chronic illnesses, such as coronary heart disease [4]. However, at the same time, consumption of fresh produce is associated with a growing number of foodborne outbreaks due to bacterial contamination of these products [5].

Leafy greens, such as lettuce, spinach, and fresh herbs, are some of the vegetables most frequently linked to bacterial infections [6]. In the United States, from 1990 to 2005, the Food Safety Project reported that at least 713 produce-related outbreaks were associated with foodborne disease, of which 12% involved fresh fruits and vegetables [4, 7]. In 2011, the Advisory Committee on the Microbiological Safety of Food (ACMSF) reported that, in the UK, there were 531 cases of reported illness, including one death, related to the consumption of fruits and vegetables between 2008 and 2010 [8]. In the same year, Germany reported an outbreak of Shiga toxin-producing E. coli (STEC) serotype O104 : H4; at the end of the outbreak, 3785 cases of illness were reported outside of Germany, identifying contaminated sprouted seeds as responsible for the foodborne outbreak [4].

It should be emphasized that the effect of foodborne diseases affects not only the sick person but also has considerable economic repercussions. On the one hand, there are costs related to the sick person, including medical care and absenteeism from work and school. On the other hand, there are the costs on society, including the decrease in worker productivity, expenses of research on the outbreak, the loss of income due to food companies closing, legal expenses for litigation related to diseases, and the expenses in public medical services [9].

It has been shown that how crops are harvested, processed, and distributed has enhanced both the supply and variety of products, which may also have increased the risk of more widespread outbreaks. The increase in illness associated with consumption of fresh produce reflects a documented increase in food contamination [10].

Foodborne illness may be the cause of fresh produce contamination by pathogenic bacteria, viruses, and protozoa [11–14]. This contamination may originate from manure, soil, sewage, surface water, or wildlife [15]; it may also occur during washing, slicing, soaking, packing, and food preparation [3]. Among the bacteria associated with foodborne illnesses are Listeria monocytogenes [16], E. coli [17], Shigella soney [18], Salmonella [19], and Staphylococcus aureus [20].

Survival and growth of these microorganisms depend on several factors, including the specific features of the microorganism, fruit ripeness, environmental conditions, plant development, bacterial resistance to the plant metabolic processes, plus harvest, and postharvest processes [21]. Particularly, some pathogenic microorganisms can internalize and adhere to the plant surface [15]. Unfortunately, current industrial sanitizing and washing treatments of fruits and vegetables (e.g., triple washing of prepackaged leafy greens) do not guarantee the total elimination of pathogens [22]. Therefore, this review considers the main E. coli pathotypes associated with foodborne outbreaks due to fresh produce consumption.

Furthermore, some recently introduced processes, considered to prevent the contamination of raw vegetables, are also described. They range from the production stages to the hygienic conditions during food preparation, from “the field to the table.” Reij and Den Aantrekker [23] reported that important factors contributing to the presence of pathogens in prepared foods are insufficient hygiene (1.6%), cross contamination (3.6%), processing or storage in inadequate rooms (4.2%), contaminated equipment (5.7%), and contamination by personnel (9.2%).

2. Incidence of E. coli

The most common vegetables associated with E. coli STEC are sprouts and green leafy vegetables (Table 1). The possible source of the contamination of sprouts is the seed that is used (it was possible to see that there were many contaminated seed lots). In the case of leafy greens, it appears that contaminated water (drag water from cattle lots or water contaminated by other sources) is the most common source of contamination. Many outbreaks reported around 30 cases, with the ratio of hospitalizations to cases ranging from 18 to 67%.

3. Contamination Factors in Fresh Vegetables

There are three types of factors that affect microbiota present in fresh products: physical, chemical, and biological. Physical factors, such as pH, temperature, and moisture, affect the growth and some metabolic activities of microbiota. Chemical factors include the availability and nutrients in vegetables that may be used by microorganisms. Finally, biological factors include the presence of competitive microbiota and bacterial-plant interactions [24]. Fresh produce may be contaminated at any point in the production chain between farm and table. It has been shown that produce contamination is high during three periods: in the field, during initial processing, and in the kitchen [25]. Table 2 lists agricultural factors (organic fertilizer, irrigation water, soil, and spraying of pesticides and insecticides) and postharvest practices (handling, collection, washing, processing, transportation, and packaging) that can cause the contamination of raw vegetables by various pathogenic microorganisms, including E. coli [12, 26–28].

3.1. Preharvest Factors

Soil and improperly composted animal manure are considered to be the main preharvest contamination factors. Soil is a natural reservoir for a large variety of human pathogens, including pathogenic E. coli, due to the addition of animal waste [29]. E. coli O157 : H7 may survive in the soil from 7 to 25 weeks depending on soil types, humidity level, and temperature. This bacterium can also survive during crop storage or distribution [30]. According to Launders et al. [31], the presence of STEC O157 in potatoes represents a risk because it may cause cross contamination with other foods that are consumed raw. Furthermore, in organic food production, the use of animal manure is a common practice; several reports relate this type of crop system to the presence of fecal contamination, particularly during the leafy vegetable harvest [32]. According to the Centers for Disease Control and Prevention (CDC) [33], several US states were affected by the consumption of organic spinach contaminated with STEC O157.

Domestic animals and wildlife also represent a potential source of pathogenic bacteria, particularly for lettuce and leafy greens at preharvest stages along the coast of California and in Yuma, AZ [34]. Berger et al. [10] showed that the feces of wildlife are involved in vegetable contamination and may cause E. coli O157 : H7 outbreaks. Jay-Russell et al. [6] studied a potential reservoir for pathogenic E. coli in feces from coyotes and dogs. Insects could also be a source of plant contamination. Contaminated flies have been shown to transfer E. coli to plant leaves or fruits [10]. In addition, Lynch et al. [18] found that intensive agricultural practices have forced crop fields to be too close to animal production areas. The ecological consequences of this proximity have increased the likelihood of contamination by E. coli O157 : H7 in wildlife: the percentages tested positive in unspecified duck was 5% (1/20 total samples) in Washington, USA; in large mammals including deer, such as the black-tailed deer (Odocoileus hemionus columbianus), it was 11.1% (1/9 total samples); in California, USA, in unspecified deer, it was 25% (1/4 total samples); in Ireland, in feral pig (Sus scrofa), it was 14.9% (13/87 total samples); in California and in small mammals in England, such as the rabbit (Oryctolagus cuniculus), it was 48.8% (20/41 total samples). All sample types were feces, anal and cloacal swabs, or gastrointestinal contents from individual animals, unless otherwise noted [35].

Seasons are another important environmental condition that affects the prevalence of E. coli in vegetables. For example, E. coli contamination in cilantro and parsley significantly increased in fall compared to that found in spring and winter [18]. The finding of E. coli in irrigation water has been associated with the presence of feces from cattle and other animals, especially during heavy rainfall.

There are current reports on outbreaks caused by the consumption of lettuce irrigated with water contaminated with E. coli O157 : H7 [36]. However, the risk associated with the use of contaminated water for irrigation depends on the irrigation system used. There is a lower probability risk of spreading pathogens from contaminated water through drip irrigation versus overhead sprinkler systems [37]. Another study shows that well water used for irrigation may be contaminated with E. coli O157 : H7 from feces of cattle or other animals, which can be observed especially during heavy rainfall. Also, karst formations occur when acidic water begins to break down bedrock surfaces, allowing surface water to enter fractures in limestone, contaminating the groundwater, which then favors the survival of E. coli in karst streams for long periods [17].

An additional factor during the handling and harvesting of crops are the workers’ hands. They can become a vehicle for contamination during preharvest due to the lack of access to latrines or handwashing stations [18].

3.2. Postharvest Contamination

In some cases, the presence of E. coli in vegetables, such as alfalfa sprouts, fresh spinach, and raw clover sprouts, is significantly higher at final postharvest stages compared to early stages of handling [38]. This may be due to subsequent direct contamination or by pathogen multiplication during postharvest procedures in raw vegetables.

The confirmation of E. coli in postharvest packing steps indicates possible fecal contamination and the potential presence of enteric pathogens of fecal origin. According to Zhang et al. [39], when E. coli O157 : H7 was isolated from certain types of fresh vegetables, the prevalence was relatively low, but this microorganism can cause illness in consumers.

Water is employed in many steps, such as washing, chill tanks, sprays, and shipping ice during the postharvest process. The washing procedure is required to remove soil and debris from vegetables and some microorganisms. In spite of this, if the water used is contaminated, washing, slicing, soaking, packaging, and preparation may be the original source of E. coli transmission to vegetables. The use of contaminated water in hydrocoolers in which fresh products are stored may generate vegetable contamination [40]. Other sources of potential contamination with E. coli during the preparation of green leafy vegetables (salads) include the water baths or dump tanks used by packers and the lack of cooling during storage [30]. In addition, food contamination may occur if the vegetables are prepared with unclean implements in restaurants or home kitchens. Lynch et al. [18] mentioned that the establishment of pathogens, such as E. coli, in vegetables may occur through cross contamination by the food handler’s hands due to poor hygiene when raw meat or poultry are also being prepared.

Some outbreaks have been associated with the cutting of vegetables during salad preparation. The fresh-cut produce used in the salads has been linked to the bacterial growth. Estrada-Garcia et al. [41] discussed the risk of acquiring an ETEC infection when chopped vegetables are used in the preparation and consumption of Mexican salsa. Due to the great diversity of possible sources of contamination in fresh vegetables, more studies are required to learn how to prevent and correct contamination during pre- and postharvest processing.

3.3. Preharvest and Postharvest Preventive Measures for Fresh Produce

During preharvest, some pathogens may be transferred to the environment by application of inadequately composted animal manure [10]. Therefore, it is essential to use fertilizers that are properly “stabilized.” One way to stabilize them is through the use of composting, in which the organic matter is decomposed by the action of microorganisms for a certain period of time (e.g., 3 or 15 days) at a designated temperature (131°F), followed by a stage of curing under colder conditions. These conditions reduce the levels of pathogenic microorganisms, promote the decomposition of cellulose and lignin, and stabilize their composition [42, 43]. Untreated human sewage should not be used to fertilize vegetables and crops for human consumption [27], unless it complies with the specifications for the use of biosolids according to regulation [44].

There is a risk of microbial contamination from water associated with irrigation systems due to the relationship between the volume of water retained on the crop’s surface, the amount of food consumed, and time harvest [45, 46]. Likewise, there is a recognized need to establish GAPs (Good Agricultural Practices) based on produce safety standard protocols for the irrigation of fresh produce [47]. During postharvest, wash water can be a transmission vehicle for pathogens, especially when this water is reused [28]. In addition, E. coli can survive for relatively long times in tap water, which can have serious consequences for the health of consumers. This point was revealed in incidents occurring in the water supply system of Walkerton, Canada, which was contaminated with E. coli O157 : H7; seven people died, and more than 2,300 people became ill [48].

In addition, the risk of reclaimed water may be reduced through treatment and disinfection systems, such as activated charcoal, reverse osmosis, membrane filtration, chlorination, ozonation, and UV irradiation; however, some systems are often expensive, particularly in developing countries [45].

Postharvest treatment of fruit and vegetables is also involved in food contamination; these treatments include handling, storage, transportation, and cleaning. Various studies reveal that food workers were frequently engaged in unsafe food handling, promoting microbial contamination of ready-to-eat foods. This typically occurs because food handlers are asymptomatic carriers of pathogenic microorganisms or have poor personal hygiene. Measures to diminish the risk of contamination by food workers include implementing proper handwashing and improving personal hygiene [20].

The World Health Organization [49] suggests 5 basic steps to prevent contamination of food by E. coli and other enteropathogens: (1) separating raw and cooked foods, (2) keeping the work area clean, (3) cook (the food thoroughly), (4) keeping food at safe temperatures, and (5) using safe water and raw materials.

Other actions to decrease food contamination are the use of better disinfectants. Recently, studies examined different and novel disinfectants for produce disinfection, such as chlorine dioxide, ozonized water, and electrolyzed oxidizing water. However, all these methods have their own limitations, making them unsuitable for an extensive application [50]. For example, ozonized water has been approved as GRAS (generally recognized as safe) by the FDA (Food and Drug Administration) as an effective disinfectant against bacteria, fungi, protozoa, and microbial spores; however, ozone is very unstable and may be toxic, causing eye and respiratory system irritation [51]. Other alternatives are those proposed by Qi et al. [50], using sodium persulfate activated by ferrous sulfate and sodium hydroxide, which effectively inactivate E. coli O157 : H7. According to the Food Safety Modernization Act (FMSA) for fresh products, food handlers should receive education on the appropriate use of sanitizing agents and on the principles of food hygiene and safety [52]. Another important measure is for managers to be well trained in microbiology, so they can properly supervise preparation of the agents. These training measures could contribute to the reduction of foodborne disease outbreaks associated with the consumption of raw vegetables.

While the most commonly used sanitizer is chlorine at 100 to 200 ppm, other alternative sanitizers, including ozone, peroxyacetic acid, and chlorine dioxide, are actively being evaluated for efficacy against pathogenic and spoilage microorganisms. Peracetic acid (80 ppm), chlorine (100 and 200 ppm), chlorine dioxide (3 and 5 ppm), and ozone (3 ppm) reduce populations >5 log of E. coli O157 : H7 inoculated on apples, lettuce, strawberries, and cantaloupe. Sensory panels only detected the use of 80 ppm peracetic acid on chopped lettuce and 200 ppm sodium hypochlorite on whole apples, with the other treatments being acceptable for consumers [53]. Angeles-Núñez [54] showed that poor hygiene in containers and transportation may be sources of contamination and may be counteracted with an adequate system of washing, disinfection, and the application of good agricultural practices. The main risk factors of contamination during transportation include following improper production practices, temperature abuse, unsanitary cargo areas, improper loading or unloading procedures, damaged packaging, shipping containers in inadequate condition, poor employee habits, and road conditions [55].

Another approach, the use of Modified Atmosphere Packaging (MAP) of fresh fruits and vegetables results in an extended shelf life. MAP systems generally utilize an internal package atmosphere other than air in a hermetically sealed package of suitable permeability. O₂, CO₂, and N₂ are the most commonly employed. The effect of MAP in inhibiting the growth of pathogens is more influenced by the type of vegetables than by the particular gas used. According to the study conducted by Abadias et al. [22], the population of E. coli O157 : H7 was higher in fresh-cut carrots (7.0–8.4 log cfu·g⁻¹) at 25°C after 3 days of storage, while in fresh-cut melon, the bacterium reached populations of 8.5 and 8.9 log cfu·g⁻¹ after 1 day of storage; in modified atmosphere packaging, no growth was observed in the fresh-cut pineapple.

As mentioned in the previous section, the food processing industry has been using chemical decontamination (hypochlorite, peroxyacetic acid, organic acid, hydrogen peroxide, trisodium phosphate, and ozone) and physical decontamination (gamma irradiation) of ready-to-eat fresh produce. However, it has been recently reported that the nonthermal method of pulsed ultraviolet (PUV) light is a more effective method for reducing EHEC biofilm on fresh produce and packaging materials. A different strategy is focused on the use of plant commensal microbiota to compete with pathogens for diffusible factors or carbon sources in vegetal leaves and roots [4, 10, 56–59].

Recent studies are focusing on improving the efficacy of antimicrobial agents by increasing the lethal activity on pathogenic microorganisms such as E. coli, specifically focusing on the toxicity of reactive oxygen species (ROS) such as superoxide, hydrogen peroxide, and hydroxyl radical. These agents usually accumulate after exposing the bacteria to a stressor agent, such as an antimicrobial. According to Hong et al. [60], the blocking of ROS accumulation by exogenous mitigating agents slowed or inhibited the E. coli poststressor death, and they concluded that the lethal action of the agents depends in part of an amplifying accumulation of ROS that exceeds primary damage repair.

4. Survival Conditions and Persistence Mechanisms

Escherichia coli is an innocuous member of the human and warm-blooded animal gut microbiota; however, pathogenic strains may cause intestinal and extraintestinal infections. These primary hosts may acquire E. coli from water and food contaminated with feces; therefore, the presence of E. coli is used as an indicator of fecal contamination.

Some E. coli strains have been isolated from various plants used for human consumption, and these plants, such as spinach, lettuce, alfalfa, cress, bean, arugula, tomato, and radish, are considered a secondary host [61–64]. These plants have physical barriers such as wax, cuticle, cell wall, trichomes, and stomata (natural pores). It has been shown that some bacteria use stomata as entrance points to the leaf interior. Several human pathogenic bacteria can survive on and penetrate the plant interior in the apoplast; they can remain in this environment with low metabolic activity, and they are able to survive drastic changes in temperature, pH, osmolality, and nutrient deprivation [65, 66].

Pathogenic E. coli possess adherence factors for human epithelial colonization, and it has been shown that several of these factors are also used for adherence to raw vegetables [67]. On the contrary, the plant offers E. coli a harsh environment with aerobic conditions, lower temperature, low pH, a high level of UV (ultraviolet) energy, and aerial surfaces (phyllosphere), which are poor in nutrients and contain antimicrobial secondary metabolites [68]. However, diarrheagenic E. coli have evolved mechanisms for vegetal attachment that vary according to the strain and plant involved (Table 3). Contamination of raw vegetables with E. coli is important since vegetables are used for fresh food preparations and since low doses of infection are sufficient to cause intestinal disease (E. coli O157 : H7 <100 or even <10) [64].

4.1. STEC E. coli O157 : H7

Verotoxigenic or Shiga-like toxigenic E. coli (VTEC or STEC) O157 : H7 is considered a large threat in foodborne diseases. E. coli O157 : H7 became the first of several strains referred to as enterohaemorrhagic E. coli or EHEC, which can produce one or more Shiga toxin (also called verocytotoxins and formerly known as Shiga-like toxins). STEC strains can survive in fresh ground beef and on fresh leafy green vegetables, and it is well known that the main reservoirs for VTEC are ruminants, which continually shed bacteria into the environment, contaminating food and water.

Various mechanisms involving adhesins, fimbriae, flagella, and the LEE-encoded effectors are typically used by VTEC for colonization and attachment [80]. LEE is a chromosomal region called the locus of enterocyte effacement that encodes a type III secretion factor (T3SS), an adhesion called intimin (eae), and the translocated receptor of intimin [81]. However, little is known about the use of these mechanisms in how VTEC is interacting with the plants as secondary hosts.

Several studies have shown that several proteins or structures are needed to colonize different plants. For example, it was reported that VTEC requires the EspA fiber of T3SS, but not pili or flagella to attach to arugula leaves [69] or the T3SS to colonize lettuce and spinach [70]. However, it needs the T3SS, flagella, curli, E. coli common pilus (ECP), and the hemorrhagic coli pilus (HCP) to colonize baby spinach leaves [71]. Curli is also implicated in the adherence of EHEC to alfalfa sprouts. This amyloid fimbria is also involved in binding to, and invasion of, human epithelial cells [72, 73].

There are several genes and/or structures associated with biofilm formation for plant colonization by STEC. These biofilms, which are formed of poly-beta-1,5-n-acetyl-D-glucosaminecellulose, cellulose, and colonic acid, are found in sprouts and tomato root segments [74]. In order to determine what type of genes are differentially expressed during the plant colonization, Crozier et al. [82] performed a transcriptomic analysis following exposure of VTEC O157 : H7 to plant extracts, specifically those of spinach (S. olercera) or lettuce (Lactuca sativa). Interestingly, genes differentially regulated are associated with metabolism, biofilm, stress response, and some unknown genes. On the contrary, genes for the pathogenicity island LEE and motility, which have a role in the pathogenicity in humans, are repressed.

E. coli O157 : H7 has the ability to colonize and internalize mainly in live spinach and lettuce plants [10, 83–86]. It can be retained (bound or entrapped) by several parts of the plant, such as leaves, sprouts, and fruit, even after vigorous washing or disinfection [61, 87–90]. For example, EHEC has the ability to adhere diffusely to the epidermis, with aggregation around the stomata, and penetration to a depth of 20 to 100 μm into the stomata and junction zones (spongy mesophyll) of cut lettuce leaves [10, 91]. In addition, it has been shown that E. coli O157 : H7 can move into the plant through the root system to reach the edible portion of lettuce [89]. In accordance with the European Food Safety Authority and the World Health Organization [49, 92], the only way to eliminate STEC from food is through heating (cooking to 70°C). On the contrary, Lu et al. [57] reported that bacteria of the E. coli group were reduced to less than 30 MPN/g, which was the safety level, when fresh-cut celery were irradiated with 1.0 kGy.

4.2. Non-O157 : H7 STEC

Although there are 200 different serotypes of STEC, few are associated with foodborne illness. In Mexico, some non-O157 STEC strains were identified in raw foods, such as vegetable salads and carrot juice [3, 93]. Some clinically relevant non-O157 : H7 serotypes are commonly called “the big six”; they include serotypes O26, O45, O103, O111, O121, and O145 [94]. In a recent study with non-O157 Shiga toxin-producing E. coli (STEC) strains that included the big six (O26, O45, O103, O111, O121, and O145), three other serogroups implicated in serious illness (O91, O113, and O128) from humans, sheep, or bovines showed the ability to form biofilms on abiotic surfaces. These strains also exhibited resistance to multiple antimicrobials [95]. This biofilm forming capability could be important for STEC persistence in the environment, and it could also contribute to the presence of reservoirs for antibiotic resistance genes.

4.3. ETEC

Enterotoxigenic E. coli, ETEC, is an important cause of infantile and travelers’ diarrhea [80]. ETEC’s virulence factors are the heat labile toxin (LT) and the heat stable toxin (ST). Both mediate deregulation of ion channels in the epithelial cell membrane [96]. ETEC can survive in a variety of environments, such as rivers, drinking water, irrigation water, and fresh vegetables [97]. It has been shown that ETEC has the ability to form biofilms through curli and extracellular matrix (1,5-n-acetyl-D-glucosaminecellulose, cellulose, and colonic acid) on sprouts and tomato roots [74, 75]. Also, ETEC adheres firmly to lettuce and leafy vegetables through flagella [76]. It has been observed that the growth of enteric pathogens such as ETEC is greater in plant tissue having mechanical damage due to availability of nutrients. Finally, ETEC in contact with various parts of the plant or its extracts can differentially regulate the expression of its genes; for example, this bacterium responds depending on its exposure to lysates or to acidic pH in vegetables [98].

4.4. EAEC

Enteroaggregative E. coli (EAEC) is the second most common cause of travelers’ diarrhea after ETEC and is associated with foodborne outbreaks of diarrhea in developing countries. The main virulence factors are the heat stable toxin (EAST1), the Shigella enterotoxin (ShET1), and hemolysin E [41]. There is a Shiga toxin-producing EAEC strain responsible for one of the largest foodborne outbreaks in Europe, the EAEC strain O104 : H4. This strain combines the chromosomal backbone of EAEC with a bacteriophage encoding Stx2 from STEC [99].

Recently, Borgersen et al. [100] found that pathogenic Shiga toxin EAEC O104 : H4 produces 3- to 6-fold higher levels of exopolysaccharide structures of colonic acid than the EAEC O42 strain. This colonic acid structure and the biofilm structures are formed on the surface of sprouts. Expression of the colonic acid capsule, in O42 and O104 : H4, is seen at room temperature, but not at 37°C. In addition, bile downregulates the expression of colonic acid. All of this suggests that EAEC exists in a “biofilm competent state” in the environment, which promotes its persistence on raw vegetables. When EAEC enters the human gastrointestinal tract, the bacterium is protected from the acid pH of the stomach by the biofilm that covers it [100]. Later, biofilm expression is downregulated by bile at 37°C, and other important virulence factors are expressed at the intestinal level. Production by colonic acid is not exclusively a property of EAEC: EHEC, EPEC, and E. coli enteroinvasive (EIEC) are also able to produce colonic acid.

EAEC also shows adherence to the arugula leaf (Eruca vesicaria) as two different phenotypes, one of small bacterial aggregates covering the entire leaf surface and the other of dense bacterial attachment to the guard cell that surrounds the stomata. Using mutant analysis, both phenotypes are explained through the aggregative adherence fimbriae (AAF) and the flagella. The flagellum mutant adheres to the epidermis but lacks stomatal tropism. In contrast, an aaf mutant lacks the ability to adhere to the epidermis while maintaining stomatal adherence. In this way, multiple adherence factors are involved in the interaction of EAEC to raw vegetables [63].

5. Conclusion

The presence of enteropathogenic bacteria in fresh produce plays an important role in the emergence of foodborne outbreaks. There are many possible sources of contamination on fresh produce due to exposure to many different environments and handling. More studies are necessary to better understand how to prevent the occurrence of E. coli on fresh produce. The attachment to plant surfaces is the first step in the colonization process and subsequent transmission of pathogens via the edible parts of plants. However, each enteropathogen has its own molecular mechanisms of adherence and fitness to the vegetable biosphere; many are similar to mechanisms used to colonize the primary host. All enteropathogens survive in fresh produce for commercially relevant periods despite the use of multiple disinfection systems. The future of food safety lies in adherence to strategies for the different categories of E. coli pathogens. These measures will help prevent bacterial transmission and benefit human health. Finally, growers, producers, packers, and food consumers need to examine their own processes and incorporate strategies for maintaining food safety.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

References

R. H. Liu, “Health benefits of fruit and vegetables are from additive and synergistic combinations of phytochemicals,” The American Journal of Clinical Nutrition, vol. 78, no. 3, pp. 517S–520S, 2003.
View at: Publisher Site | Google Scholar
M. L. Luna-Guevara, J. J. Luna-Guevara, P. Hernández-Carranza, H. Ruíz-Espinosa, and C. E. Ochoa-Velasco, “Phenolic compounds: a good choice against chronic degenerative diseases,” in Studies in Natural Products Chemistry, vol. 59, pp. 79–108, Elsevier, Amsterdam, The Netherlands, 2019.
View at: Google Scholar
J. Castro-Rosas, J. F. Cerna-Cortés, E. Méndez-Reyes, D. Lopez-Hernandez, C. A. Gómez-Aldapa, and T. Estrada-Garcia, “Presence of faecal coliforms, Escherichia coli and diarrheagenic E. coli pathotypes in ready-to-eat salads, from an area where crops are irrigated with untreated sewage water,” International Journal of Food Microbiology, vol. 156, no. 2, pp. 176–180, 2012.
View at: Publisher Site | Google Scholar
C. Goodburn and C. A. Wallace, “The microbiological efficacy of decontamination methodologies for fresh produce: a review,” Food Control, vol. 32, no. 2, pp. 418–427, 2013.
View at: Publisher Site | Google Scholar
R. M. Callejón, M. I. Rodríguez-Naranjo, C. Ubeda, R. Hornedo-Ortega, M. C. Garcia-Parrilla, and A. M. Troncoso, “Reported foodborne outbreaks due to fresh produce in the United States and European Union: trends and causes,” Foodborne Pathogens and Disease, vol. 12, no. 1, pp. 32–38, 2015.
View at: Publisher Site | Google Scholar
M. T. Jay-Russell, A. F. Hake, Y. Bengson, A. Thiptara, and T. Nguyen, “Prevalence and characterization of Escherichia coli and Salmonella strains isolated from stray dog and coyote feces in a major leafy greens production region at the United States-Mexico border,” PLoS One, vol. 9, no. 11, Article ID e113433, 2014.
View at: Publisher Site | Google Scholar
Food and Drug Administration, Produce Safety from Production to Consumption: 2004 Action Plan to Minimize Foodborne Illness Associated with Fresh Produce Consumption, Food and Drug administration, Maryland, MD, USA, 2004.
Advisory committee on the microbiological safety of food. Annual Report 2011.
L. Luna-Guevara, J. J. Luna-Guevara, and M. G. Spencer, El ABC para la Seguridad Alimentaria en los Hogares, Editorial Educacion y Cultura, Mexico, 2015.
C. N. Berger, S. V. Sodha, R. K. Shaw et al., “Fresh fruit and vegetables as vehicles for the transmission of human pathogens,” Environmental Microbiology, vol. 12, no. 9, pp. 2385–2397, 2010.
View at: Publisher Site | Google Scholar
M. S. Alam, F. Feroz, H. Rahman, K. K. Das, and R. Noor, “Microbiological contamination sources of freshly cultivated vegetables,” Nutrition & Food Science, vol. 45, no. 4, pp. 646–658, 2015.
View at: Publisher Site | Google Scholar
M. H. Iturriaga, M. L. Tamplin, and E. F. Escartín, “Colonization of tomatoes by Salmonella Montevideo is affected by relative humidity and storage temperature,” Journal of Food Protection, vol. 70, no. 1, pp. 30–34, 2007.
View at: Publisher Site | Google Scholar
L. J. Harris, J. N. Farber, L. R. Beuchat et al., “Outbreaks associated with fresh produce: incidence, growth, and survival of pathogens in fresh and fresh-cut produce,” Comprehensive Reviews in Food Science and Food Safety, vol. 2, no. s1, pp. 78–141, 2003.
View at: Publisher Site | Google Scholar
S. E. Bilek and F. Turantaş, “Decontamination efficiency of high power ultrasound in the fruit and vegetable industry, a review,” International Journal of Food Microbiology, vol. 166, no. 1, pp. 155–162, 2013.
View at: Publisher Site | Google Scholar
C. Liu, N. Hofstra, and E. Franz, “Impacts of climate change on the microbial safety of pre-harvest leafy green vegetables as indicated by Escherichia coli O157 and Salmonella spp,” International Journal of Food Microbiology, vol. 163, no. 2-3, pp. 119–128, 2013.
View at: Publisher Site | Google Scholar
Q. Zhu, R. Gooneratne, and M. A. Hussain, “Listeria monocytogenes in fresh produce: outbreaks, prevalence and contamination levels,” Foods, vol. 6, no. 3, 2017.
View at: Publisher Site | Google Scholar
K. E. Heiman, R. K. Mody, S. D. Johnson, P. M. Griffin, and L. H. Gould, “Escherichia coli O157 outbreaks in the United States, 2003–2012,” Emerging Infectious Diseases, vol. 21, no. 8, pp. 1293–1301, 2015.
View at: Publisher Site | Google Scholar
M. F. Lynch, R. V. Tauxe, and C. W. Hedberg, “The growing burden of foodborne outbreaks due to contaminated fresh produce: risks and opportunities,” Epidemiology and Infection, vol. 137, no. 3, pp. 307–315, 2009.
View at: Publisher Site | Google Scholar
A. Mba-Jonas, W. Culpepper, T. Hill et al., “A multistate outbreak of human Salmonella Agona infections associated with consumption of fresh, whole papayas imported from Mexico-United States, 2011,” Clinical Infectious Diseases, vol. 66, no. 11, pp. 1756–1761, 2018.
View at: Publisher Site | Google Scholar
D. Faour-Klingbeil, M. Murtada, V. Kuri, and E. C. D. Todd, “Understanding the routes of contamination of ready-to-eat vegetables in the Middle East,” Food Control, vol. 62, pp. 125–133, 2016.
View at: Publisher Site | Google Scholar
K. R. Matthews, “Leafy vegetables,” in The Produce Contamination Problem. Causes and Solutions, K. R. Matthews, G. M. Sapers, and C. P. Gerba, Eds., Elsevier, Amsterdam, The Netherlands, 2014.
View at: Google Scholar
M. Abadias, I. Alegre, M. Oliveira, R. Altisent, and I. Viñas, “Growth potential of Escherichia coli O157:H7 on fresh-cut fruits (melon and pineapple) and vegetables (carrot and escarole) stored under different conditions,” Food Control, vol. 27, no. 1, pp. 37–44, 2012.
View at: Publisher Site | Google Scholar
M. W. Reij and E. D. Den Aantrekker, “Recontamination as a source of pathogens in processed foods,” International Journal of Food Microbiology, vol. 91, no. 1, pp. 1–11, 2004.
View at: Publisher Site | Google Scholar
S. Sela, “Microbial quality and safety of fresh produce,” in Postharvest Handling: A Systems Approach, Academic Press, Cambridge, MA, USA, 2009.
View at: Google Scholar
E. C. Ailes, J. S. Leon, L.-A. Jaykus et al., “Microbial concentrations on fresh produce are affected by postharvest processing, importation, and season,” Journal of Food Protection, vol. 71, no. 12, pp. 2389–2397, 2008.
View at: Publisher Site | Google Scholar
L. R. Beuchat, “Ecological factors influencing survival and growth of human pathogens on raw fruits and vegetables,” Microbes and Infection, vol. 4, no. 4, pp. 413–423, 2002.
View at: Publisher Site | Google Scholar
A. Rajwar, P. Srivastava, and M. Sahgal, “Microbiology of fresh produce: route of contamination, detection methods, and remedy,” Critical Reviews in Food Science and Nutrition, vol. 56, no. 14, pp. 2383–2390, 2016.
View at: Publisher Site | Google Scholar
R. Huang, D. de Vries, and H. Chen, “Strategies to enhance fresh produce decontamination using combined treatments of ultraviolet, washing and disinfectants,” International Journal of Food Microbiology, vol. 283, pp. 37–44, 2018.
View at: Publisher Site | Google Scholar
J. M. Whipps, P. Hand, D. A. C. Pink, and G. D. Bending, “Chapter 7 human pathogens and the phyllosphere,” Advances in Applied Microbiology, vol. 64, pp. 183–221, 2008.
View at: Publisher Site | Google Scholar
E. A. Duffy, L. M. Lucia, J. M. Kells, A. Castillo, S. D. Pillai, and G. R. Acuff, “Concentrations of Escherichia coli and genetic diversity and antibiotic resistance profiling of Salmonella isolated from irrigation water, packing shed equipment, and fresh produce in Texas,” Journal of Food Protection, vol. 68, no. 1, pp. 70–79, 2005.
View at: Publisher Site | Google Scholar
N. Launders, M. E. Locking, M. Hanson et al., “A large Great Britain-wide outbreak of STEC O157 phage type 8 linked to handling of raw leeks and potatoes—corrigendum,” Epidemiology and Infection, vol. 144, no. 1, p. 182, 2016.
View at: Publisher Site | Google Scholar
N. Denis, H. Zhang, A. Leroux, R. Trudel, and H. Bietlot, “Prevalence and trends of bacterial contamination in fresh fruits and vegetables sold at retail in Canada,” Food Control, vol. 67, pp. 225–234, 2016.
View at: Publisher Site | Google Scholar
Centers for Disease Control and Prevention, “Ongoing multistate outbreak of Escherichia coli serotype O157:H7 infections associated with consumption of fresh spinach-United States, September 2006,” MMWR. Morbidity and Mortality Weekly Report, vol. 55, no. 38, pp. 1045-1046, 2006.
View at: Google Scholar
D. Stuart, C. Shennan, and M. Brown, “Food safety versus environmental protection on the Central California coast: exploring the science behind an apparent conflict,” in Center for Agroecology and Sustainable Food Systems, University of California Santa Cruz, Santa Cruz, CA, USA, 2006.
View at: Google Scholar
J. A. LAnghoLz and M. T. Jay-Russell, “Potential role of wildlife in pathogenic contamination of fresh produce,” Human-Wildlife Interactions, vol. 7, no. 1, p. 14, 2013.
View at: Google Scholar
Centers for Disease Control and Prevention, Multistate Outbreak of E. coli O157:H7 Infections Linked to Romaine Lettuce, 2018, https://www.cdc.gov/ecoli/2018/o157h7-04-18/index.html18/index.
R. Mitra, E. Cuesta-Alonso, A. Wayadande, J. Talley, S. Gilliland, and J. Fletcher, “Effect of route of introduction and host cultivar on the colonization, internalization, and movement of the human pathogen Escherichia coli O157:H7 in spinach,” Journal of Food Protection, vol. 72, no. 7, pp. 1521–1530, 2009.
View at: Publisher Site | Google Scholar
C. Frank, “Epidemic profile of Shiga-toxin-producing Escherichia coli O104:H4 outbreak in Germany,” The New England Journal of Medicine, vol. 365, no. 19, pp. 1771–1780, 2011.
View at: Google Scholar
G. Zhang, Y. Chen, L. Hu et al., “Survey of foodborne pathogens, aerobic plate counts, total coliform counts, and Escherichia coli counts in leafy greens, sprouts, and melons marketed in the United States,” Journal of Food Protection, vol. 81, no. 3, pp. 400–411, 2018.
View at: Publisher Site | Google Scholar
J. V. Gagliardi, P. D. Millner, G. Lester, and D. Ingram, “On-farm and postharvest processing sources of bacterial contamination to melon rinds,” Journal of Food Protection, vol. 66, no. 1, pp. 82–87, 2003.
View at: Publisher Site | Google Scholar
T. Estrada-Garcia, J. F. Cerna, M. R. Thompson, and C. Lopez-Saucedo, “Faecal contamination and enterotoxigenic Escherichia coli in street-vended chili sauces in Mexico and its public health relevance,” Epidemiology and Infection, vol. 129, no. 1, pp. 223–226, 2002.
View at: Publisher Site | Google Scholar
Food and Drugs, Chapter I. Food and Drug Administration Department of Health and Human Services Subchapter C. Food for Human Consumption. Part 112-Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption. Subpart C-Personnel Qualifications and Training, US Food and Drugs Administration, Silver Spring, MA, USA, 2019, https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?CFRPart=112.
Food and Drugs, Chapter I. Food and Drug Administration Department of Health and Human Services Subchapter C. Food for Human Consumption. Part 112-Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption. Subpart F-Biological Soil Amendments of Animal Origin and Human Waste, US Food and Drugs Administration, Silver Spring, MA, USA, 2019, , 2019, https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?fr=112.54.
EPA 40 CFR 503, Standards for the Use or Disposal of Sewage Sludge, Subpart D—Pathogens and Vector Attraction Reduction, United States Environmental Protection Agency, Washington, DC, USA, 2015, , 2015, http://www.ecfr.gov/cgibin/textidx?SID=cb309f2da2aba12c1d4e50233633c3e1&node=sp40.30.5d6.
A. J. Hamilton, F. Stagnitti, R. Premier, A.-M. Boland, and G. Hale, “Quantitative microbial risk assessment models for consumption of raw vegetables irrigated with reclaimed water,” Applied and Environmental Microbiology, vol. 72, no. 5, pp. 3284–3290, 2006.
View at: Publisher Site | Google Scholar
S. F. Tyrrel, J. W. Knox, and E. K. Weatherhead, “Microbiological water quality requirements for salad irrigation in the United Kingdom,” Journal of Food Protection, vol. 69, no. 8, pp. 2029–2035, 2006.
View at: Publisher Site | Google Scholar
Y. Pachepsky, D. R. Shelton, J. E. T. McLain, J. Patel, and R. E. Mandrell, “Irrigation waters as a source of pathogenic microorganisms in produce: a review,” Advances in Agronomy, vol. 113, pp. 75–141, 2011.
View at: Publisher Site | Google Scholar
J. De Jesús Alba, “Riesgos microbiológicos en agua de bebida: una revisión clínica,” Química Viva, vol. 12, no. 3, pp. 215–233, 2013.
View at: Google Scholar
World Health Organization, 2018, https://www.who.int/news-room/fact-sheets/detail/e-coli.
H. Qi, Q. Huang, and Y.-C. Hung, “Efficacy of activated persulfate in inactivating Escherichia coli O157:H7 and Listeria monocytogenes,” International Journal of Food Microbiology, vol. 284, pp. 40–47, 2018.
View at: Publisher Site | Google Scholar
K. Joshi, R. Mahendran, K. Alagusundaram, T. Norton, and B. K. Tiwari, “Novel disinfectants for fresh produce,” Trends in Food Science & Technology, vol. 34, no. 1, pp. 54–61, 2013.
View at: Publisher Site | Google Scholar
Food and Drugs, Chapter I. Food and Drug Administration Department of Health and Human Services Subchapter C. Food for Human Consumption. Part 112-Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption, Subpart D-Health and Hygiene, 2019, https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?CFRPart=112.
S. L. Rodgers, J. N. Cash, M. Siddiq, and E. T. Ryser, “A comparison of different chemical sanitizers for inactivating Escherichia coli O157:H7 and Listeria monocytogenes in solution and on apples, lettuce, strawberries, and cantaloupe,” Journal of Food Protection, vol. 67, no. 4, pp. 721–731, 2004.
View at: Publisher Site | Google Scholar
J. G. Angeles-Núñez, “Análisis de la calidad sanitaria de nopal verdura en Otumba, Estado de México,” Revista mexicana de ciencias agricolas, vol. 5, pp. 129–141, 2014.
View at: Google Scholar
N. Ackerley, A. Sertkaya, and R. Lange, “Food transportation safety: characterizing risks and controls by use of expert,” Food Protection Trends, vol. 30, no. 4, pp. 212–222, 2010.
View at: Google Scholar
L. Beuchat and J. H. Ryu, “Produce handling and processing practices,” Emerging Infectious Diseases, vol. 3, no. 4, pp. 459–465, 1997.
View at: Publisher Site | Google Scholar
Z. Lu, Z. Yu, X. Gao, F. Lu, and L. Zhang, “Preservation effects of gamma irradiation on fresh-cut celery,” Journal of Food Engineering, vol. 67, no. 3, pp. 347–351, 2005.
View at: Publisher Site | Google Scholar
N. L. Montgomery and P. Banerjee, “Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes in biofilms by pulsed ultraviolet light,” BMC Research Notes, vol. 8, no. 1, p. 235, 2015.
View at: Publisher Site | Google Scholar
K. M. Wright, L. Crozier, J. Marshall, B. Merget, A. Holmes, and N. J. Holden, “Differences in internalization and growth of Escherichia coli O157:H7 within the apoplast of edible plants, spinach and lettuce, compared with the model species Nicotiana benthamiana,” Microbial Biotechnology, vol. 10, no. 3, pp. 555–569, 2017.
View at: Publisher Site | Google Scholar
Y. Hong, J. Zeng, X. Wang, K. Drlica, and X. Zhao, “Post-stress bacterial cell death mediated by reactive oxygen species,” Proceedings of the National Academy of Sciences, vol. 116, no. 20, pp. 10064–10071, 2019.
View at: Publisher Site | Google Scholar
E. Franz, A. Visser, A. Vandiepeningen, M. Klerks, A. Termorshuizen, and A. Vanbruggen, “Quantification of contamination of lettuce by GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium,” Food Microbiology, vol. 24, no. 1, pp. 106–112, 2007.
View at: Publisher Site | Google Scholar
J. Jablasone, K. Warriner, and M. Griffiths, “Interactions of Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes plants cultivated in a gnotobiotic system,” International Journal of Food Microbiology, vol. 99, no. 1, pp. 7–18, 2005.
View at: Publisher Site | Google Scholar
C. N. Berger, R. K. Shaw, F. Ruiz-Perez et al., “Interaction of enteroaggregative Escherichia coli with salad leaves,” Environmental Microbiology Reports, vol. 1, no. 4, pp. 234–239, 2009.
View at: Publisher Site | Google Scholar
M. L. Ackers, B. E. Mahon, E. Leahy et al., “An outbreak of Escherichia coli O157:H7 infections associated with leaf lettuce consumption,” The Journal of Infectious Diseases, vol. 177, no. 6, pp. 1588–1593, 1998.
View at: Publisher Site | Google Scholar
L.-D. Dinu and S. Bach, “Induction of viable but nonculturable Escherichia coli O157:H7 in the phyllosphere of lettuce: a food safety risk factor,” Applied and Environmental Microbiology, vol. 77, no. 23, pp. 8295–8302, 2011.
View at: Publisher Site | Google Scholar
M. D. Winfield and E. A. Groisman, “Role of nonhost environments in the lifestyles of Salmonella and Escherichia coli,” Applied and Environmental Microbiology, vol. 69, no. 7, pp. 3687–3694, 2003.
View at: Publisher Site | Google Scholar
J. D. Barak, L. Gorski, P. Naraghi-Arani, and A. O. Charkowski, “Salmonella enterica virulence genes are required for bacterial attachment to plant tissue,” Applied and Environmental Microbiology, vol. 71, no. 10, pp. 5685–5691, 2005.
View at: Publisher Site | Google Scholar
M. T. Brandl, “Fitness of human enteric pathogens on plants and implications for food safety,” Annual Review of Phytopathology, vol. 44, no. 1, pp. 367–392, 2006.
View at: Publisher Site | Google Scholar
R. K. Shaw, C. N. Berger, B. Feys, S. Knutton, M. J. Pallen, and G. Frankel, “Enterohemorrhagic Escherichia coli exploits EspA filaments for attachment to salad leaves,” Applied and Environmental Microbiology, vol. 74, no. 9, pp. 2908–2914, 2008.
View at: Publisher Site | Google Scholar
J. Xicohtencatl-Cortes, E. S. Chacón, Z. Saldaña, E. Freer, and J. A. Girón, “Interaction of Escherichia coli O157:H7 with leafy green produce,” Journal of Food Protection, vol. 72, no. 7, pp. 1531–1537, 2009.
View at: Publisher Site | Google Scholar
Z. Saldaña, E. Sánchez, J. Xicohtencatl-Cortes, J. L. Puente, and J. A. Girón, “Surface structures involved in plant stomata and leaf colonization by shiga-toxigenic Escherichia coli O157:H7,” Frontiers in Microbiology, vol. 2, p. 119, 2011.
View at: Publisher Site | Google Scholar
J. D. Barak, L. C. Whitehand, and A. O. Charkowski, “Differences in attachment of Salmonella enterica serovars and Escherichia coli O157:H7 to alfalfa sprouts,” Applied and Environmental Microbiology, vol. 68, no. 10, pp. 4758–4763, 2002.
View at: Publisher Site | Google Scholar
A. G. Torres, C. Jeter, W. Langley, and A. G. Matthysse, “Differential binding of Escherichia coli O157:H7 to alfalfa, human epithelial cells, and plastic is mediated by a variety of surface structures,” Applied and Environmental Microbiology, vol. 71, no. 12, pp. 8008–8015, 2005.
View at: Publisher Site | Google Scholar
A. G. Matthysse, R. Deora, M. Mishra, and A. G. Torres, “Polysaccharides cellulose, poly-beta-1,6-N-Acetyl-D-Glucosamine, and colanic acid are required for optimal binding of Escherichia coli O157:H7 strains to alfalfa sprouts and K-12 strains to plastic but not for binding to epithelial cells,” Applied and Environmental Microbiology, vol. 74, no. 8, pp. 2384–2390, 2008.
View at: Publisher Site | Google Scholar
C. Beloin, A. Roux, and J.-M. Ghigo, “Escherichia coli biofilms,” Current Topics in Microbiology and Immunology, vol. 322, pp. 249–289, 2008.
View at: Publisher Site | Google Scholar
R. K. Shaw, C. N. Berger, M. J. Pallen, Å. Sjöling, and G. Frankel, “Flagella mediate attachment of enterotoxigenic Escherichia coli to fresh salad leaves,” Environmental Microbiology Reports, vol. 3, no. 1, pp. 112–117, 2011.
View at: Publisher Site | Google Scholar
M. Bielaszewska, A. Mellmann, W. Zhang et al., “Characterisation of the Escherichia coli strain associated with an outbreak of haemolytic uraemic syndrome in Germany, 2011: a microbiological study,” The Lancet Infectious Diseases, vol. 11, no. 9, pp. 671–676, 2011.
View at: Publisher Site | Google Scholar
Y. Itoh, Y. Sugita-Konishi, F. Kasuga et al., “Enterohemorrhagic Escherichia coli O157:H7 present in radish sprouts,” Applied and Environmental Microbiology, vol. 64, no. 4, pp. 1532–1535, 1998.
View at: Google Scholar
Y. Jung, H. Jang, and K. R. Matthews, “Effect of the food production chain from farm practices to vegetable processing on outbreak incidence,” Microbial Biotechnology, vol. 7, no. 6, pp. 517–527, 2014.
View at: Publisher Site | Google Scholar
M. A. Croxen, R. J. Law, R. Scholz, K. M. Keeney, M. Wlodarska, and B. B. Finlay, “Recent advances in understanding enteric pathogenic Escherichia coli,” Clinical Microbiology Reviews, vol. 26, no. 4, pp. 822–880, 2013.
View at: Publisher Site | Google Scholar
E. Franz and A. H. van Bruggen, “Ecology of E. coli O157:H7 and Salmonella enterica in the primary vegetable production chain,” Critical Reviews in Microbiology, vol. 34, no. 3-4, pp. 143–161, 2008.
View at: Publisher Site | Google Scholar
L. Crozier, P. E. Hedley, J. Morris et al., “Whole-transcriptome analysis of verocytotoxigenic Escherichia coli O157:H7 (sakai) suggests plant-species-specific metabolic responses on exposure to spinach and lettuce extracts,” Front Microbiol, vol. 7, p. 1088, 2016.
View at: Publisher Site | Google Scholar
R. M. Chalmers, H. Aird, and F. J. Bolton, “Waterborne Escherichia coli O157,” Journal of Applied Microbiology, vol. 88, no. S1, pp. 124S–132S, 2000.
View at: Publisher Site | Google Scholar
I. T. Kudva, K. Blanch, and C. J. Hovde, “Analysis of Escherichia coli O157:H7 survival in ovine or bovine manure and manure slurry,” Applied and Environmental Microbiology, vol. 64, no. 9, pp. 3166–3174, 1998.
View at: Google Scholar
G. Wang, T. Zhao, and M. P. Doyle, “Fate of enterohemorrhagic Escherichia coli O157:H7 in bovine feces,” Applied and Environmental Microbiology, vol. 62, no. 7, pp. 2567–2570, 1996.
View at: Google Scholar
K. M. Wright, S. Chapman, K. McGeachy et al., “The endophytic lifestyle of Escherichia coli O157:H7: quantification and internal localization in roots,” Phytopathology, vol. 103, no. 4, pp. 333–340, 2013.
View at: Publisher Site | Google Scholar
L. R. Beuchat, “Survival of enterohemorrhagic Escherichia coli O157:H7 in bovine feces applied to lettuce and the effectiveness of chlorinated water as a disinfectant,” Journal of Food Protection, vol. 62, no. 8, pp. 845–849, 1999.
View at: Publisher Site | Google Scholar
P. J. Taormina and L. R. Beuchat, “Behavior of enterohemorrhagic Escherichia coli O157:H7 on alfalfa sprouts during the sprouting process as influenced by treatments with various chemicals,” Journal of Food Protection, vol. 62, no. 8, pp. 850–856, 1999.
View at: Publisher Site | Google Scholar
E. B. Solomon, S. Yaron, and K. R. Matthews, “Transmission of Escherichia coli O157:H7 from contaminated manure and irrigation water to lettuce plant tissue and its subsequent internalization,” Applied and Environmental Microbiology, vol. 68, no. 1, pp. 397–400, 2002.
View at: Publisher Site | Google Scholar
C. Jeter and A. G. Matthysse, “Characterization of the binding of diarrheagenic strains of E. coli to plant surfaces and the role of curli in the interaction of the bacteria with alfalfa sprouts,” Molecular Plant-Microbe Interactions, vol. 18, no. 11, pp. 1235–1242, 2005.
View at: Publisher Site | Google Scholar
K. H. Seo and J. F. Frank, “Attachment of Escherichia coli O157:H7 to lettuce leaf surface and bacterial viability in response to chlorine treatment as demonstrated by using confocal scanning laser microscopy,” Journal of Food Protection, vol. 62, no. 1, pp. 3–9, 1999.
View at: Publisher Site | Google Scholar
European Food Safety Authority, 2011, https://www.efsa.europa.eu/en/press/news/110609.
M. D. R. Torres-Vitela, C. A. Gómez Aldapa, J. F. Cerna-Cortes, A. Villarruel-López, E. Rangel-Vargas, and J. Castro-Rosas, “Presence of indicator bacteria, diarrhoeagenic Escherichia coli pathotypes and Salmonella in fresh carrot juice from Mexican restaurants,” Letters in Applied Microbiology, vol. 56, no. 3, pp. 180–185, 2013.
View at: Publisher Site | Google Scholar
R. Wang, J. L. Bono, N. Kalchayanand, S. Shackelford, and D. M. Harhay, “Biofilm formation by Shiga toxin-producing Escherichia coli O157:H7 and Non-O157 strains and their tolerance to sanitizers commonly used in the food processing environment,” Journal of Food Protection, vol. 75, no. 8, pp. 1418–1428, 2012.
View at: Publisher Site | Google Scholar
J. Wang, K. Stanford, T. A. McAllister et al., “Biofilm formation, virulence gene profiles, and antimicrobial resistance of nine serogroups of non-O157 shiga toxin-Producing Escherichia coli,” Foodborne Pathogens and Disease, vol. 13, no. 6, pp. 316–324, 2016.
View at: Publisher Site | Google Scholar
J. M. Fleckenstein, P. R. Hardwidge, G. P. Munson, D. A. Rasko, H. Sommerfelt, and H. Steinsland, “Molecular mechanisms of enterotoxigenic Escherichia coli infection,” Microbes and Infection, vol. 12, no. 2, pp. 89–98, 2010.
View at: Publisher Site | Google Scholar
E. MacDonald, K. E. Møller, A. L. Wester et al., “An outbreak of enterotoxigenic Escherichia coli (ETEC) infection in Norway, 2012: a reminder to consider uncommon pathogens in outbreaks involving imported products,” Epidemiology and Infection, vol. 143, no. 3, pp. 486–493, 2015.
View at: Publisher Site | Google Scholar
J. L. Kyle, C. T. Parker, D. Goudeau, and M. T. Brandl, “Transcriptome analysis of Escherichia coli O157:H7 exposed to lysates of lettuce leaves,” Applied and Environmental Microbiology, vol. 76, no. 5, pp. 1375–1387, 2010.
View at: Publisher Site | Google Scholar
F. Scheutz, E. M. Nielsen, J. Frimodt-Møller et al., “Characteristics of the enteroaggregative Shiga toxin/verotoxin-producing Escherichia coli O104:H4 strain causing the outbreak of hemolytic uraemic syndrome in Germany, May to June 2011,” Eurosurveillance, vol. 16, no. 24, 2011.
View at: Publisher Site | Google Scholar
Q. Borgersen, D. T. Bolick, G. L. Kolling et al., “Abundant production of exopolysaccharide by EAEC strains enhances the formation of bacterial biofilms in contaminated sprouts,” Gut Microbes, vol. 9, no. 2, pp. 264–278, 2018.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2019 J. J. Luna-Guevara et al. 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.

PDF Download Citation

Download other formats

Order printed copies

Views

15734

Downloads

5789

Citations