Saito, S., et al
Detection and characterization of β-lactamase genes in a total of ten non-typhoidal Salmonella (NTS) clinical isolates exhibiting resistance to the third-generation cephalosporins collected during 2012 -2014 in Japan were conducted. Among five strains with cefotaxime MIC (minimum inhibitory concentration) ≥64 μg/ml and positive results of clavulanic acid inhibition effect, blaCTX-M-2 was detected in three strains (serotypes Stanley and Muenchen), and each of blaTEM-52 (serotype Manhattan) and blaSHV-12 (serotype Infantis) was found in one strain. The blaCMY-2 was detected in all of the remaining five strains (serotypes Infantis, Rissen, Newport, and Saintpaul) with cefotaxime MICs of 4 to 32 μg/ml and positive results of cloxacillin- and 3-aminophenylboronic acid-based inhibition tests. ISEcp1 was located upstream of the blaCMY-2 in four strains and of the blaCTX-M-2 in one strain. Incompatibility (Inc) A/C, Inc P, and Inc I1 plasmids were present in strains harboring blaCMY-2 which were detected predominantly in this study. Acquisition of resistance to the third-generation cephalosporins by invasive NTS may well limit therapeutic options for severe systemic infections, and would cause serious public health problem. Though such resistant clinical isolates are still rare in Salmonella species in Japan, our findings revealed the presence of cephem-resistant NTS among food handlers, thus underline the necessity of more systematic nationwide investigation.
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