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

Non-beta-lactam inhibitor-based methods were evaluated for detecting plasmid-mediated AmpC β-lactamases in Klebsiella spp., Escherichia coli , and Proteus mirabilis . Using CLSI methodology and disks containing cefotetan alone and in combination with 400 μg 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 β-lactamases in AmpC producers.