Expression of blaA and blaB and Susceptibility to Penicillins and Cephalosporins in Yersinia enterocolitica from Different Foods

Objective: Yersinia enterocolitica which is an important foodborne pathogen causing illness in humans is an extremely heterogeneous species consisting of different subtypes. It has the intrinsic resistance to β-lactam antibiotics because of the production of β-lactamases, BlaA and BlaB. Y. enterocolitica exhibits variable susceptibilities to β-lactams. Materials and Methods: The expression of the blaA and blaB genes by polymerase chain reaction, and the susceptibility to some β-lactams including penicillins and cephalosporins using the broth microdilution and disk diffusion methods were determined. A total of 18 Y. enterocolitica isolates were examined. Results: Overall, 33.3% of these isolates carried the blaA and blaB genes, all of which were recovered from chicken meat. The wide range of MIC for ampicillin (≤2-128 µg/mL) and ceftazidime (≤0.0625-2 µg/mL) was also observed. Of the Y. enterocolitica isolates, 55.6% were resistant to ampicillin (≥32 µg/mL) while the remaining isolates (44.4%) were susceptible to ampicillin (≤ 8 µg/mL). All isolates were susceptible to ceftazidime at the concentration tested. According to the disk diffusion test, 55.6% and 33.3% of the isolates were resistant to ticarcillin and cefoxitin, respectively. No resistance to piperacillin and ceftriaxone was found. Conclusion: The results showed that the presence of the blaA and blaB genes and intrinsic resistance against penicillins and cephalosporins were variable among Y. enterocolitica food isolates. Furthermore, the blaA and blaB genes were expressed in most of the resistant isolates to β-lactams, which may indicate the contribution of the genes to the drug resistance.