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. 2005 Aug;43(8):4163-7.
doi: 10.1128/JCM.43.8.4163-4167.2005.

Inhibitor-based methods for detection of plasmid-mediated AmpC beta-lactamases in Klebsiella spp., Escherichia coli, and Proteus mirabilis

Philip E Coudron  1
Affiliations

Inhibitor-based methods for detection of plasmid-mediated AmpC beta-lactamases in Klebsiella spp., Escherichia coli, and Proteus mirabilis

Philip E Coudron. J Clin Microbiol. 2005 Aug.

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.

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Figures

FIG. 1.
FIG. 1.
Comparison of the standard confirmatory disk test for ESBL and the boronic acid (bor) disk test for AmpC β-lactamase with two K. pneumoniae control strains. Strain ATCC 700603 produced ESBL and no AmpC β-lactamase, and strain R154 produced AmpC β-lactamase and no ESBL. CAZ, ceftazidime; CAZ CLAV, ceftazidime and clavulanic acid; CTT, cefotetan; CTT + bor, cefotetan and 400 μg of boronic acid.
FIG. 2.
FIG. 2.
Comparison of the confirmatory ESBL test using the standard ceftazidime and ceftazidime/clavulanic disks and the same two disks, each with a second disk, containing 400 μg of boronic acid (bor), placed on top. The K. pneumoniae isolate harbored both an ESBL and an AmpC β-lactamase.
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