Molecular epidemiology of extended-spectrum β-lactamases and Escherichia coli isolated from retail foods including chicken meat in Japan

Contamination of retail meat with extended-spectrum β-lactamase (ESBL)-producing Escherichia coli has been reported, but only limited data have been documented in Japan. One hundred fifty-three retail foods including chicken meat, beef, pork, and vegetables were purchased from 29 supermarkets between January and October in 2010. ESBL producers were recovered from each food sample using McConkey agar plate supplemented with 1 mg/L of cefotaxime. ESBL type was identified by DNA sequencing analysis after polymerase chain reaction amplification. Antibiogram, O serotype, plasmid replicon type, pulsotype, and multilocus sequence type were also determined. Fifty-two epidemiologically unrelated Escherichia coli isolates producing ESBL were recovered from 35 (22.9%) of 153 samples, all of which were chicken meat. ESBL types were mainly CTX-M-2 group followed by CTX-M-1 group and CTX-M-8 group. The numbers of bacterial isolates (8 of 21, 38.1%) harboring bla_CTX-M-8 recovered from imported meat samples were significantly larger than those of domestic ones (one of 31, 3.2%) (p<0.05). Nine O serotypes (mainly O8, O25, and O1) were found, together with O-antigen untypable (OUT). Four E. coli belonging to the O25b:H4-ST131 clone were recovered from domestic (n=1) and imported meat samples (n=3), respectively. These four isolates were susceptible to fluoroquinolones, although the E. coli O25b:H4-ST131 clone producing CTX-M-15, which is predominant in human isolates, is usually resistant to fluoroquinolones. By contrast, five CTX-M-15-producing E. coli strains were recovered only from domestic meat samples, and their serotypes were O8 or OUT instead of predominant serotype O25b. Our results showed that ESBL-producing E. coli isolates recovered from retail chicken meat samples in Japan are generally divergent in both genetic and serological aspects. Further comparative analyses of bla _CTX-M-mediating genetic elements would be continued in the next step to characterize the ESBL producers from retail foods in Japan.