Phenotypic and Genotypic Identification of Four Cases of Plasmid-Mediated AmpC β-Lactamases-Producing Escherichia coli Admitted to a Tertiary Centre

We describe four patients with a positive culture of AmpC β-lactamases-producing Escherichia coli (E. coli), despite the fact that our understanding of plasmid-mediated AmpC β-lactamases (pAmpC) is currently limited. Three out of four cases of AmpC β-lactamases-producing Escherichia coli were isolated from a urine sample, and one was from a peritoneal fluid sample. All four isolates are resistant to cefoxitin disc and were subjected to a confirmatory AmpC phenotypic test (AmpC induction test) and monoplex polymerase chain reaction (PCR) for the determination of six pAmpC genotypes (blaDHA, blaEBC, blaMOX, blaFOX, blaACC, and blaCIT). All four E. coli isolates tested negative for the AmpC induction test, while monoplex PCR analysis was positive only for the blaDHA pAmpC genotype and negative for all five other genotypes (blaEBC, blaMOX, blaFOX, blaACC, and blaCIT). A common clinical characteristic across all patients was fever. One patient was treated for perforated sigmoid diverticulitis, while the other three patients were treated for acute pyelonephritis or urinary tract infections (UTIs). Each patient improved significantly and was successfully discharged.