Journal Article

Evaluation of a new cefepime–clavulanate ESBL Etest to detect extended-spectrum β-lactamases in an Enterobacteriaceae strain collection

Enno Stürenburg, Ingo Sobottka, Djahesh Noor, Rainer Laufs and Dietrich Mack

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 54, issue 1, pages 134-138
Published in print July 2004 | ISSN: 0305-7453
Published online July 2004 | e-ISSN: 1460-2091 | DOI:
Evaluation of a new cefepime–clavulanate ESBL Etest to detect extended-spectrum β-lactamases in an Enterobacteriaceae strain collection

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  • Medical Oncology
  • Critical Care


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Objectives: In this study, we evaluated the performance of a new ESBL Etest configuration based on clavulanate synergy with cefepime compared with cefotaxime–clavulanate and ceftazidime–clavulanate ESBL Etest strips for the detection of extended-spectrum β-lactamases (ESBL) in an Enterobacteriaceae strain collection, with special focus on Enterobacter spp.

Methods: Overall, a total of 54 clinical isolates of ESBL-producing Enterobacteriaceae species were evaluated: Enterobacter aerogenes (n=3), Enterobacter cloacae (n=10), Escherichia coli (n=10), Klebsiella oxytoca (n=3), Klebsiella pneumoniae (n=25) and Proteus mirabilis (n=3). To check Etest behaviour with resistance phenotypes similar to ESBL, our panel was expanded by six clinical isolates of K. oxytoca that were identified as putative producers of their chromosomal K1 β-lactamase.

Results: With this panel, ESBL Etest was 98% sensitive with cefepime–clavulanate, 83% with cefotaxime–clavulanate, and 74% with ceftazidime–clavulanate strips. Concentrating on Enterobacter spp., reliable ESBL detection could only be achieved by the new cefepime–clavulanate strip since it confirmed ESBL production in all strains (100% sensitivity) whereas only 4/13 (31%) of Enterobacter strains were positive using cefotaxime–clavulanate or ceftazidime–clavulanate strips. A limitation of using the new cefepime strip was less than optimal specificity with K1 phenotypes of K. oxytoca: among six strains, four isolates were scored false-positive by Etest strips containing cefepime–clavulanate.

Conclusion: The new Etest ESBL strip containing cefepime–clavulanate is a valuable supplement to current methods for detection of ESBLs. In our study collection, the cefepime–clavulanate strip was the best configuration for detection of ESBLs, particularly in Enterobacter spp.

Keywords: ESBL detection; Etest methodology

Journal Article.  2839 words.  Illustrated.

Subjects: Medical Oncology ; Critical Care

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