Drug-resistance due to AmpC β-lactamases represents a growing problem worldwide. In this study, a previously collected sample of 108 cefoxitin-resistant clinical isolates was assessed for AmpC β-lactamase production through routine phenotypic testing and double-disc cefoxitin/cloxcallin (DD-CC), cefoxitin/phenylboronic acid (CDT-PBA) and AmpC disc tests. The same isolates were characterized by a novel multiplex polymerase chain reaction molecular assay to detect the presence of blaACT, blaDHA, blaCIT, blaFOX, blaMIR and blaMOX. By phenotypic analysis, 56%, 55% and 48 % were detected as being AmpC β-lactamase producers by the CDT-PBA, DD-CC and AmpC disc tests, respectively. By molecular analysis, 57 % were determined to be AmpC β-lactamase producers, including 34 % blaFOX, 8 % blaCIT and 1.6 % blaDHAas mono-AmpC producers. The production of multiple AmpC molecular types was common, including 30 % with both blaCIT+FOX and 1.6 % each of blaCIT+DHA, blaACT+MIR, blaACT+FOX, blaACT+DHA and blaMIR+FOX. Molecular characterization of AmpC would help detect the prevalence of AmpC β-lactamase producers, facilitate proper patient management and implement infection control practices.
Keywords: AmpC disk test; Cefoxtin-Cloxcallin; Molecular characterization; ampC β-lactamases; cefoxitin-resistance.