Cephalosporin resistance mechanisms in Escherichia coli isolated from raw chicken imported into the UK

We characterized mechanisms of resistance to oxyimino-cephalosporins in Escherichia coli isolated from raw chicken meat imported into the UK from South America, to ascertain whether this foodstuff contributes to the dissemination in the UK of extended-spectrum beta-lactamase (ESBL)-producing E. coli belonging to the international uropathogenic ST131 clone. Sampling and collection of imported raw chicken meat was performed in accordance with regulatory guidelines by the London Port Health Authority at Tilbury. E. coli strains producing ESBLs were isolated based on growth within the zones of cefpodoxime (10 mu g) discs. MICs were determined by agar dilution and interpreted using BSAC/EUCAST breakpoints. PCR was used to determine the phylogenetic groups of E. coli, to detect ESBL genes and to determine the incompatibility groups of plasmids encoding CTX-M enzymes. The molecular environments surrounding bla(CTX-M) were determined by DNA sequencing and PCR mapping. A total of 141 oxyimino-cephalosporin-resistant E. coli were isolated from 62 of 210 batches of imported raw chicken sampled. Thirty percent of these isolates produced group 2 CTX-M ESBLs, 27% produced group 8 CTX-M ESBLs, 42% produced CMY-type AmpC enzymes and 1% produced a group 2 CTX-M along with a CMY enzyme; none produced CTX-M-15 ESBL and none belonged to the ST131 clone. In contrast to human clinical ESBL E. coli, > 90% of isolates were susceptible to ciprofloxacin and 74% to all aminoglycosides. Raw chicken imported into the UK from South America commonly carries ESBL-producing E. coli, but is not a significant source for the ST131 clone or for the CTX-M-15 ESBL.