Molecular Characterization and Occurrence of Extended-Spectrum β-Lactamase Resistance Genes among Salmonella enterica Serovar Corvallis from Thailand, Bulgaria, and Denmark

Fifty nine Salmonella Corvallis isolates from humans and food products in Bulgaria, Denmark, and Thailand were examined for antimicrobial susceptibility and characterized by pulsed-field gel electrophoresis (PFGE). Cephalosporin-resistant isolates were examined for the presence of genes encoding β-lactamases by PCR and sequencing. Ten different PFGE types were observed. One type (30 isolates) was recovered in all three countries; three types were found only in Bulgaria, two only in Denmark, two only in Thailand, and two both in Denmark and Thailand. Ten isolates were susceptible to all antimicrobial agents tested, whereas 41 were resistant to three or more antimicrobials. Most resistance was observed among the isolates from Bulgaria. Of the 25 isolates from Bulgaria, 20 displayed resistance to ampicillin and the cephalosporins ceftiofur and cephalothin. All 20 isolates tested negative for bla CMY-1, bla CMY-2, and bla ACC, but positive for bla SHV, of which five were sequenced to bla SHV-2. Plasmid profil...