Journal Article

Cefepime and the inoculum effect in tests with <i>Klebsiella pneumoniae</i> producing plasmid-mediated AmpC-type β-lactamase

Cheol-In Kang, Hyunjoo Pai, Sung-Han Kim, Hong-Bin Kim, Eui-Chong Kim, Myoung-don Oh and Kang-Won Choe

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 54, issue 6, pages 1130-1133
Published in print December 2004 | ISSN: 0305-7453
Published online December 2004 | e-ISSN: 1460-2091 | DOI:
Cefepime and the inoculum effect in tests with Klebsiella pneumoniae producing plasmid-mediated AmpC-type β-lactamase

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Objective: In the past decade, a new problem in Klebsiella pneumoniae strains has emerged: plasmid-mediated AmpC enzymes. This study was conducted to investigate the activity of cefepime against clinical isolates by determining the activities of cefepime and three other parenteral β-lactam agents in standard and high inoculum MIC tests.

Methods: A total of 61 K. pneumoniae blood isolates, including 28 isolates producing AmpC-type β-lactamases (14 isolates of DHA-1 and 14 isolates of CMY-1-like) and 33 isolates producing extended-spectrum β-lactamases (ESBLs) (32 isolates of TEM- or SHV-related and one isolate of CTX-M-14-like), were included in the study. Antimicrobial susceptibilities were determined using broth microdilution MIC tests with standard and 100-fold-higher inocula. The inoculum effect was defined as an eight-fold or greater MIC increase on testing with the higher inoculum.

Results: In tests with AmpC β-lactamase-producing K. pneumoniae isolates and their transconjugants, the inoculum effect was most consistently detected with cefepime, cefotaxime and ceftazidime, as inoculum effects were consistently detected in ESBL-producing isolates. However, the inoculum effect was least frequently detected with imipenem.

Conclusion: Although the inoculum effect is an in vitro laboratory phenomenon, these results suggest that cefepime may be a less than reliable agent for therapy in cases of high inoculum infections caused by AmpC β-lactamase-producing K. pneumoniae.

Keywords: K. pneumoniae; cephalosporins; β-lactam resistance

Journal Article.  1969 words. 

Subjects: Medical Oncology ; Critical Care

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