Diversity of extended-spectrum β-lactamases and class C β-lactamases among cloacal Escherichia coli isolates in Belgian broiler farms

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 beta-lactam antibiotics and other antimicrobial agents by using disk diffusion tests. Three different beta-lactam resistance phenotypes suggested the presence of an extended-spectrum beta-lactamase (ESBL), a class C beta-lactamase, or the combination of an ESBL with a class C beta-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 beta-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 beta-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 beta-lactamase (CW-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 beta-lactamases among these isolates is high, and they may act as a reservoir of ESBL and ampC genes.