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Antimicrobial Agents and Chemotherapy, April 2008, p. 1238-1243, Vol. 52, No. 4
0066-4804/08/$08.00+0     doi:10.1128/AAC.01285-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Diversity of Extended-Spectrum β-Lactamases and Class C β-Lactamases among Cloacal Escherichia coli Isolates in Belgian Broiler Farms

Department of Bacteriology and Immunology, CODA-CERVA-VAR, Groeselenberg 99, 1180 Brussels, Belgium,¹ Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium,² Department of Reproduction, Obstetrics and Herd Health, Veterinary Epidemiology Unit, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B-9820 Merelbeke, Belgium,³ Institute for Agricultural and Fisheries Research, Unit Technology and Food, Brusselsesteenweg 370, B-9090 Melle, Belgium,⁴ Scientific Institute of Public Health, J. Wytsmanstraat 14, 1050 Brussel, Belgium⁵

Received 5 October 2007/ Returned for modification 28 November 2007/ Accepted 16 January 2008

A total of 295 ceftiofur-resistant Escherichia coli isolates were obtained from 489 cloacal samples collected at five different Belgian broiler farms with the aim to evaluate the diversity of this resistance at the farm level. Strains were examined for resistance against β-lactam antibiotics and other antimicrobial agents by using disk diffusion tests. Three different β-lactam resistance phenotypes suggested the presence of an extended-spectrum β-lactamase (ESBL), a class C β-lactamase, or the combination of an ESBL with a class C β-lactamase. Seventy-six percent of these isolates also showed acquired resistance to other antimicrobial agents. After genotyping by repetitive extragenic palindromic-PCR, 51 unrelated E. coli strains were selected for further analyses. Isoelectric focusing and sequencing of the amplicons obtained in PCRs for the detection of genes encoding broad-spectrum β-lactamase enzymes revealed the following ESBLs: TEM-52 (13.2%), TEM-106 (2%), CTX-M-1 (27.4%), CTX-M-2 (7.8%), CTX-M-14 (5.9%), and CTX-M-15 (2%). The only plasmidic AmpC β-lactamase found in this study was the CMY-2 enzyme (49%). Mutations in the promoter and attenuator regions of the chromosomal ampC gene were found only in association with bla_CMY-2 genes and ESBL genes. The combination of an ESBL (CTX-M-1) with a plasmidic AmpC β-lactamase (CMY-2) was found in 7.8% of the isolates. These data show that ceftiofur-resistant E. coli strains are often present in cloacal samples of broilers at the farm level in Belgium. The diversity of broad-spectrum β-lactamases among these isolates is high, and they may act as a reservoir of ESBL and ampC genes.

Published ahead of print on 28 January 2008.