Molecular and Phenotypic Study of Carbapenem Resistant E. coli

Background: Carbapenem resistance is an emerging problem. The aim of the present study was to determine the prevalence of carbapenem resistance and ESBLs among clinical isolates of E. coli by phenotypic methods and to study the molecular bases of the resistance by polymerase chain reaction (PCR). Methods: The study was carried on 153 non repetitive E. coli strains collected from different clinical samples from Baghdad hospitals. The strains were isolated according to standard microbiological procedures and identified by Gram stain and biochemical reactions. E. coli strains were subjected to antimicrobial susceptibility tests by the disc diffusion method, carbapenem screening, ESBL screening tests, and molecular studies for genes responsible for such resistance. Results: The study was carried out on 153 non repetitive E. coli. Detection of ESBLs by the double disc method reveals that 63 isolates (41.2%) of isolated E. coli had ESBL activity. Carbapenem resistance among E. coli reveals that 30 isolates (19.6%) had both metallo-P-lactamase and carbapenemase activity as detected by double disc synergy test and boronic acid disc. Among 63 isolates of E. coli with positive double disc tests for ESBL resistance, the most frequent gene detected by PCR was b1aTEM (52.4%), followed by b1aSHV (33.3%) and blaCTX-M (14.3%). Among 30 E. coli strains with metallo-P-lactamase activity and carbapenemase activity, the most frequent genes were IMP, VIM (30% for each), followed by NDM (20%), GIM, SIM, SPM, and KPC (10% for each). Isolated E. coli with carbapenem resistance represented 47.6% of E. coli with ESBL activity. Conclusions: The present study highlights the incidence of carbapenemase among clinical isolates of E. coli combined with extended P-lactamases activity. Phenotypic screening methods were valuable for detection of different types of resistance. The common genes responsible for carbapenem resistance were IMP, VIM, and NDM. Further studies are recommended with more included E. coli isolates.