Phenotypical-genotypical investigation of metallo-β-lactamases identified from clinical gram-negative bacilli and phylogenetical analysis of isolates

Carbapenems have become the most frequently used antibiotics in the treatment of multi-drug resistant Gram-negative bacterial infections. One of the major mechanisms of carbapenem resistance is the production of metallo-β-lactamases (MBLs). MBL genes can reside on chromosome or plasmids and easily spread among bacterial species and strains. Therefore, data on the epidemiology of antimicrobial resistance due to MBLs is critically important in the determination of antibiotic policies and therapeutic decisions. In this study in Çukurova University, Faculty of Medicine, Department of Medical Microbiology, between March 1st, 2014 and September 5th, 2015, the aim was to determine by phenotypical methods the antibacterial drug susceptibility patterns of carbapenem-resistant Gram-negatives isolated from a variety of clinical infections, to determine the enzymes associated with resistance by using genotypical methods and to analyze their clonal relatedness by PFGE. Four hundred-fifty carbapenem resistant Gram-negative bacilli isolated from patients admitted in various clinical wards were tested. The in vitro antimicrobial resistance of bacteria was determined by the disk diffusion method according to Clinical and Laboratory Standards Institute (CLSI) guidelines. One hundred thirty isolates tested positive for the production of metallo-β-lactamases by the combined disk test and the modified Hodge test. The most frequent resistance among the strains included in the present study was observed against meropenem with a rate of 99.23%, while the lowest prevalence was obtained against colistin with 5.38 %. After analyzing the carbapenem resistance genetic detdrminants, the most dominant carbapenemase genes were OXA-51, OXA-23-like and OXA-24-like. NDM, TEM, VIM and GES were found to be responsible from carbapenem resistance in both Enterobacteriaceae and non-fermenter species. In addition, after the analysis of clonal relationship by PFGE, the isolates identified as closely related were observed to be persistent, settled in different wards of our hospital, and responsible for a wide range of hospital-acquired infections. Resistance to carbapenems associated with different genetic determinants is largely diffuse in our healthcare settings. The only reliable antibiotic in infections caused by carbapenem resistant Gram-negative bacilli appears to be colistin. A wise use of antibiotics by implementing a strict antibiotic stewardship is necessary to control further dissemination of multiresistance.