Inhibitor-Based Methods for Detection of Plasmid-Mediated AmpC β-Lactamases in <i>Klebsiella</i> spp., <i>Escherichia coli</i> , and <i>Proteus mirabilis</i>

Abstract

Non-beta-lactam inhibitor-based methods were evaluated for detecting plasmid-mediated AmpC beta-lactamases in Klebsiella spp., Escherichia coli, and Proteus mirabilis. Using CLSI methodology and disks containing cefotetan alone and in combination with 400 mug of boronic acid, 9 of 10 positive control strains and 54 of 55 AmpC-PCR-positive clinical isolates were detected. Importantly 71% and 40% of these clinical isolates were susceptible by routine testing to ceftriaxone and ceftazidime, respectively. Boronic acid disks also enhanced detection of expanded-spectrum beta-lactamases in AmpC producers.