The spread of multidrug resistant (MDR) Gram negative bacteria (GNB), especially carbapenem-resistant- (CR-) Klebsiellapneumoniae and other Enterobacteriaceae, CR Acinetobacterbaumannii and MDR Pseudomonasaeruginosa, has become a major problem worldwide, with a high impact on both morbidity and mortality.

The choice of the most appropriate therapy against infections due to these organisms is a formidable challenge, with combination therapy appearing to be more beneficial than monotherapy in patients at high risk of death. Nevertheless, the best combined regimen has not been found and the resistance to colistin, often a last resort therapeutic option, has also been increasingly reported. New agents with activity against MDR GNB that will be available in the near future show restricted/preferential activity against certain type of carbapenemases and the clinical impact of these novel antimicrobial agents has yet to be determined.

In this challenging scenario, the microbiology laboratory plays a critical role. In fact, traditional antimicrobial susceptibility reports may no longer suffice to provide optimal information. Susceptibility profiling may need to evolve to include alternative methods such as synergy testing. Target-based molecular detection of known mutations also may no longer suffice for MDR pathogens and other profiling methods may need to be developed.

Given the complexity in the management and control of MDR GNB infections, a multidisciplinary approach appears to be recommended, one that involves clinicians, the laboratory, clinical pharmacologists, and an antimicrobial stewardship program.

Based on these assumptions, the aim of this special issue is to focus on the interaction between lab and clinic with regard to infections due to MDR GNB. In particular, we encourage submission of original articles showing the interplay between microbiological, pharmacological, and clinical studies in patients with infections due to MDR GNB. Contributions investigating the role of nonantibiotic compounds (i.e., essential oils, phages, and antimicrobials peptides) against MDR GNB and their potential use in the clinic are also welcome. Also encouraged are review articles describing the current state of art with regard to invitro and invivo as well as clinical studies in the field of MDR GNB infections. Finally, case reports suggesting a novel diagnostic or therapeutic strategy against MDR GNB infections are invited.

Potential topics include but are not limited to the following:

• Elucidation of resistance mechanisms with translational implications for antimicrobial or other therapeutic modalities
• Invitro studies on synergistic activity of different antimicrobial combinations against MDR GNB
• Therapeutic options in the setting of colistin resistance
• Different therapeutic strategies against MDR GNB infections: monotherapy, combination therapy, or innovative therapeutic strategies
• Strategies for administration of colistin and newer antimicrobials
• PK/PD characteristics of antimicrobials
• Antibacterial activity of nonantibiotic compounds against MDR GNB
• Role of the lab in infection-control practices and antimicrobial stewardships initiatives
• Strategies for laboratory testing and result reporting of MDR GNB
• Impact of laboratory antibiogram reporting on antimicrobial stewardship efforts
• New diagnostic methods for detection of MDR GNB
• Treatment strategies for Helicobacter pylori infections