Characterization of plasmid-mediated versus non-plasmid-mediated bacterial antibiotic resistance in Escherichia coli isolate

Introduction: Pathogenic bacteria contain extrachromosomal DNA called plasmids that carry many important genes, encoding factors, that help the bacteria induce disease. Among these plasmid-mediated phenotypes of medical importance is the spread of antibiotic resistance genes. These bacterial plasmid-mediated metabolic functions can be eliminated from bacterial species by plasmid curing techniques. Understanding which functions are carried by plasmids and understanding how bacteria gain these plasmids is vital. Aims and objectives: The aim of the study was to differentiate between plasmid-mediated and non-plasmid-mediated antibiotic resistance in a clinical isolate of Escherichia coli compared with its cured derivative. Materials and methods: Clinical isolates of E. coli from patients with urinary tract infections were subjected to antimicrobial susceptibility tests at the Saqr Hospital laboratory (Ras Al Khaimah, United Arab Emirates) using the Kirby – Bauer disc diffusion method. To differentiate between plasmid-mediated and non-plasmid-mediated antibiotic resistance, the E. coli isolates were then cured by growing them at an elevated temperature. The non-cured and cured samples were sent to the AccuVisBio® lab in Abu Dhabi, United Arab Emirates, for molecular analysis. The presence of a plasmid and its size were determined using the Plasmid MiniPrep Kit (Norgen Biotek Corp., Ontario, Canada) and the resultant plasmid bands were visualized using agarose gel electrophoresis. Results: The E. coli isolates showed resistance to cloxacillin, ampicillin, cephalexin, penicillin V, erythromycin, vancomycin, cephalothin, oxacillin, nalidixic acid and clindamycin, which did not change after plasmid curing. Analysis of cured and non-cured samples showed either no plasmid present or a very low copy number. Conclusion: In this clinical isolate of E. coli, resistance to cloxacillin, ampicillin, cephalexin, penicillin V, erythromycin, vancomycin, cephalothin, oxacillin, nalidixic acid and clindamycin is not plasmid mediated and is either chromosomal or results from other structural characteristics of the bacteria.