Evaluation of CHROMagar CTX, a novel medium for isolating CTX-M-ESBL-positive Enterobacteriaceae while inhibiting AmpC-producing strains
Open Access
- 19 November 2008
- journal article
- research article
- Published by Oxford University Press (OUP) in Journal of Antimicrobial Chemotherapy
- Vol. 63 (2), 302-308
- https://doi.org/10.1093/jac/dkn485
Abstract
The aim of this study was to evaluate CHROMagar CTX (CHROMagar France), a novel agar for the selective isolation of Enterobacteriaceae expressing the blaCTX-M gene in the presence of enteric bacteria expressing AmpC enzymes. A panel of 150 Gram-negative bacteria (mainly Escherichia coli, Enterobacter, Klebsiella, Pseudomonas and Salmonella) isolated from humans and animals were assembled for the purpose of evaluating CHROMagar CTX and comparing it with CHROMagar ECC with the addition of 1, 2, 4 and 8 mg/L cefotaxime or ceftazidime and with bioMérieux extended-spectrum β-lactamase (ESBL)-Bx agar. CHROMagar CTX was also assessed for its ability to isolate blaCTX-M strains from farm animal faeces (n = 342). The panel contained CTX-M-positive (n = 70) strains (CTX-M types 1, 9, 14 and 15), ESBLs (n = 31) belonging to other families (OXA, PER, SHV, TEM, VEB), strains positive for ampC genes (n = 31), strains that overexpressed ampC (n = 6), non-ESBL/AmpC strains (n = 11) and Klebsiella oxytoca (n = 1). CHROMagar CTX was superior to other agars tested for selective isolation of Enterobacteriaceae expressing the blaCTX-M gene with 100% sensitivity and 64.2% specificity for CTX-M strains in the panel and 90.1% of the colonies from animal faeces plated on CHROMagar CTX were CTX-M strains. CHROMagar CTX is a valuable agar in situations where it is important to isolate blaCTX-M strains in the presence of AmpC strains. The agar may be particularly useful in veterinary studies, where AmpC-producing commensal E. coli can be encountered reasonably frequently in the enteric flora of some animal species and may also be useful, following further evaluation, for samples from humans.Keywords
This publication has 14 references indexed in Scilit:
- Evaluation of a New Selective Chromogenic Agar Medium for Detection of Extended-Spectrum β-Lactamase-Producing EnterobacteriaceaeJournal of Clinical Microbiology, 2007
- CTX-M: changing the face of ESBLs in EuropeJournal of Antimicrobial Chemotherapy, 2006
- Escherichia coli Producing CTX-M β-Lactamases in Food Animals in Hong KongMicrobial Drug Resistance, 2006
- Longitudinal Farm Study of Extended-Spectrum β-Lactamase-Mediated ResistanceJournal of Clinical Microbiology, 2006
- Detection of Multiple Cephalosporin-ResistantEscherichia colifrom a Cattle Fecal Sample in Great BritainMicrobial Drug Resistance, 2005
- Evaluation of a new screen agar plate for detection and presumptive identification of Enterobacteriaceae producing extended-spectrum β-lactamasesDiagnostic Microbiology and Infectious Disease, 2005
- False-positive extended-spectrum -lactamase tests for Klebsiella oxytoca strains hyperproducing K1 -lactamaseJournal of Antimicrobial Chemotherapy, 2004
- Growing Group of Extended-Spectrum β-Lactamases: the CTX-M EnzymesAntimicrobial Agents and Chemotherapy, 2004
- Detection of CMY-2, CTX-M-14, and SHV-12 β-Lactamases in Escherichia coli Fecal-Sample Isolates from Healthy ChickensAntimicrobial Agents and Chemotherapy, 2003
- Detection of Plasmid-Mediated AmpC β-Lactamase Genes in Clinical Isolates by Using Multiplex PCRJournal of Clinical Microbiology, 2002