Detection of CMY-2 AmpC β-lactamase-producing enterohemorrhagic Escherichia coli O157:H7 from outbreak strains in a nursery school in Japan.

In 2013, an outbreak of enterohemorrhagic Escherichia coli (EHEC) O157:H7 occurred in a nursery school in Japan. The outbreak affected 12 school children and five members of their families. All 17 isolates obtained from these individuals were found to be clonal, as determined by pulsed-field gel electrophoresis analysis and multilocus variable number tandem repeat analysis. The antimicrobial susceptibility profiles of the isolates to 20 drugs were examined, with three isolates showing resistance to the extended-spectrum cephalosporins (ESC) and cephamycin, including cefotaxime, ceftazidime, and cefminox. The resistant isolates carried the blaCMY-2 AmpC β-lactamase gene. It is proposed that the ESC-resistant EHEC O157:H7 isolates might have acquired the resistance plasmid encoding the blaCMY-2 gene during human to human infection in the nursery school.