Abstract
β-lactamase genes were detected and characterized from 10 non-typhoidal Salmonella (NTS) clinical isolates resistant to third-generation cephalosporins collected between 2012 and 2014 in Japan. Five strains showed cefotaxime minimum inhibitory concentration (MIC) ≥ 64 μg/ml and positive clavulanic acid inhibition results. The blaCTX-M-2 was detected in 3 strains (serotypes Stanley and Muenchen), whereas blaTEM-52 (serotype Manhattan) and blaSHV-12 (serotype Infantis) were each found in 1 strain. blaCMY-2 was detected in the remaining 5 strains (serotypes Infantis, Rissen, Newport, and Saintpaul) with cefotaxime MICs of 4–32 μg/ml and positive cloxacillin- and 3-aminophenylboronic acid- based inhibition tests. ISEcp1 was located upstream of the blaCMY-2 in 4 strains and of the blaCTX-M-2 in 1 strain. Incompatibility (Inc)A/C, IncP, and IncI1 plasmids were present in the strains harboring blaCMY-2, which were detected predominantly in this study. Acquisition of resistance to third-generation cephalosporins by invasive NTS may limit therapeutic options for severe systemic infections and causing serious public health problems. Though such resistant clinical isolates are still rare in Salmonella species in Japan, our findings reveal the presence of cephem-resistant NTS in food handlers, thus emphasizing the necessity of more systematic nationwide investigations.
