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Detection of AmpC beta-lactamase in Escherichia coli: comparison of three phenotypic confirmation assays and genetic analysis


Peter-Getzlaff, S; Polsfuss, S; Poledica, M; Hombach, M; Giger, J; Böttger, E C; Zbinden, R; Bloemberg, G V (2011). Detection of AmpC beta-lactamase in Escherichia coli: comparison of three phenotypic confirmation assays and genetic analysis. Journal of Clinical Microbiology, 49(8):2924-2932.

Abstract

Two mechanisms account for AmpC activity in E. coli: mutations in the ampC promoter and attenuator regions resulting in ampC overexpression and/or acquisition of plasmid-encoded ampC genes. In this study we analyzed 51 clinical E. coli isolates with reduced susceptibility to amoxicillin/clavulanic acid, piperacillin/tazobactam or third generation cephalosporins for the presence of AmpC production. Three phenotypic AmpC confirmation assays (cefoxitin/cloxacillin disk diffusion test, cefoxitin/EDTA disk diffusion test, AmpC ETest) were compared for the detection of AmpC activity. All 51 isolates were genetically characterized by mutation analysis of the chromosomal ampC promoter/attenuator region and by PCR detection of plasmid-encoded ampC genes. Altogether, 21/51 (41 %) E. coli isolates were considered true AmpC producers. AmpC activity due to chromosomal ampC promoter/attenuator mutations was found in 12/21 strains, plasmid-encoded ampC genes were detected in 8/21 isolates. 1/21 strains contained both, ampC promoter mutations and a plasmid-encoded ampC gene. All three phenotypic tests were able to detect the majority (>90%) of AmpC positive strains correctly. Cefoxitin resistance was found to be a discriminative parameter, detecting 20/21 AmpC producing strains. Susceptibility to third generation cephalosporines, e.g. ceftriaxone, cetazidime and cefotaxime, was found in 9 of the 21 AmpC positive strains. When considering the elevated zone diameter breakpoints of the 2010 CLSI guidelines 2/21 AmpC positive strains were categorized susceptible to third generation cephalosporines.

Abstract

Two mechanisms account for AmpC activity in E. coli: mutations in the ampC promoter and attenuator regions resulting in ampC overexpression and/or acquisition of plasmid-encoded ampC genes. In this study we analyzed 51 clinical E. coli isolates with reduced susceptibility to amoxicillin/clavulanic acid, piperacillin/tazobactam or third generation cephalosporins for the presence of AmpC production. Three phenotypic AmpC confirmation assays (cefoxitin/cloxacillin disk diffusion test, cefoxitin/EDTA disk diffusion test, AmpC ETest) were compared for the detection of AmpC activity. All 51 isolates were genetically characterized by mutation analysis of the chromosomal ampC promoter/attenuator region and by PCR detection of plasmid-encoded ampC genes. Altogether, 21/51 (41 %) E. coli isolates were considered true AmpC producers. AmpC activity due to chromosomal ampC promoter/attenuator mutations was found in 12/21 strains, plasmid-encoded ampC genes were detected in 8/21 isolates. 1/21 strains contained both, ampC promoter mutations and a plasmid-encoded ampC gene. All three phenotypic tests were able to detect the majority (>90%) of AmpC positive strains correctly. Cefoxitin resistance was found to be a discriminative parameter, detecting 20/21 AmpC producing strains. Susceptibility to third generation cephalosporines, e.g. ceftriaxone, cetazidime and cefotaxime, was found in 9 of the 21 AmpC positive strains. When considering the elevated zone diameter breakpoints of the 2010 CLSI guidelines 2/21 AmpC positive strains were categorized susceptible to third generation cephalosporines.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Institute of Medical Microbiology
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:2011
Deposited On:22 Jul 2011 12:04
Last Modified:07 Dec 2017 08:39
Publisher:American Society for Microbiology
ISSN:0095-1137
Free access at:PubMed ID. An embargo period may apply.
Publisher DOI:https://doi.org/10.1128/JCM.00091-11
PubMed ID:21653764

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