Prevalence and Epidemiological Relationship of CMY-2 AmpC β-Lactamase and CTX-M Extended-Spectrum β-Lactamase-Producing Escherichia coli Isolates from Broiler Farms in Japan

To evaluate the prevalence of extended-spectrum cephalosporin (ESC)-resistant Enterobacteriaceae in broiler chickens, 41 rectal samples taken from 4 commercial farms were examined. Desoxytholate hydrogen sulfide lactose agars, supplemented with either 4 mu g/m/ cefotaxime or 16 mu g/ml ceftazidime, were used to screen ESC-resistant bacteria. ESC-resistant bacteria were isolated from all samples. Of the 164 ESC-resistant bacteria (included 4 isolates per a sample), 163 were Escherichia coli, while 1 isolate was identified as Enterobacter cloacae. Extended-spectrum beta-lactamase (ESBL) genes and plasmid-mediated AmpC beta-lactamase genes in the isolates were determined by PCR and sequencing. One AmpC beta-lactamase gene, bla(CMY-2) (66%), and 4 ESBL genes, bla(CTX-M-1), (26%), bla(CTX-M-55) (10%), bla(SHV-5) (4%) and bla(CTX-M-2) (3%), were detected in the E. coli isolates. The epidemiological relationship of the CMY-2 and CTX-M beta-lactamase-producing isolates among the farms was analyzed by pulsed-field gel electrophoresis using the Xbal restriction enzyme. Forty-one (Y1-Y41) and 14 (X1-X14) clusters were found in the CMY-2 and CTX-M-carrying E. coli isolates, respectively. Some clusters included isolates derived from more than 1 farm, indicating some cross-contamination of clonal strains and spread of CMY-2 AmpC beta-lactamase or CTX-M ESBL among the farms.