MOLECULAR DETECTION OF ANTIBIOTIC RESISTANCE GENES AND SUSCEPTIBILITY IN SERINE AND METALLO-Β-LACTAMASE PRODUCING E. COLI

Abstract

Antimicrobial resistance (AMR) has emerged as one of the most serious global public health threats, significantly increasing morbidity, mortality, and healthcare expenditures worldwide. Multidrug-resistant (MDR) Gram-negative bacteria, particularly Escherichia coli, are of major clinical concern due to their ability to acquire and disseminate β-lactamase enzymes that inactivate β-lactam antibiotics. Carbapenems are often considered last-resort agents for severe infections; however, the emergence of carbapenem-resistant E. coli, especially those producing metallo-β-lactamases (MBLs), severely limits therapeutic options. In addition to MBLs, other β-lactamases such as extended-spectrum β-lactamases (ESBLs) and serine β-lactamases (e.g., SHV-type enzymes) contribute to resistance patterns, complicating treatment strategies. The present study aimed to investigate the molecular detection of antibiotic resistance genes and evaluate antibiotic susceptibility profiles among serine and metallo-β-lactamase-producing E. coli isolates. A total of 20 clinical isolates were collected from diverse patient specimens, including urine, blood cultures, catheter tips, and endotracheal tube secretions, at BJ Micro Lab in collaboration with Abasyn University, Islamabad. Identification of E. coli isolates was performed using standard morphological and biochemical methods. Antimicrobial susceptibility testing was conducted using the Kirby–Bauer disc diffusion method according to established clinical guidelines. Phenotypic detection of MBL production was carried out using the imipenem–EDTA combined disc test (IMP-EDTA CDT), while genotypic confirmation of resistance genes, including MBL and SHV genes, was performed using multiplex polymerase chain reaction (PCR). Antibiotic susceptibility results demonstrated that 10 out of 14 evaluated isolates (71.4%) exhibited resistance to carbapenems, whereas 4 isolates (28.6%) remained susceptible. Among the carbapenem-resistant isolates, one strain (10%) carried the MBL gene, and five strains (50%) harbored the SHV gene. Notably, none of the imipenem-sensitive isolates possessed genes associated with MBL production. A high level of concordance was observed between phenotypic detection using IMP-EDTA CDT and genotypic confirmation by PCR, supporting the reliability of combined diagnostic approaches. The detection of MBL- and SHV-producing E. coli underscores a significant clinical challenge due to limited effective treatment options and the potential for rapid dissemination of resistance determinants. Early molecular identification of resistance genes, particularly in carbapenem-susceptible isolates, is essential for guiding appropriate antimicrobial therapy, strengthening infection control measures, and reducing the spread of multidrug-resistant organisms in healthcare settings.