Expression of beta-lactamases in Yersinia enterocolitica strains of biovars 2, 4 and 5

Characteristic patterns of susceptibility to beta-lactam antibiotics are as sociated with different biovars of Yersinia enterocolitica, To elucidate th e basis for these differences, the beta-lactamases of strains of Y. enteroc olitica biovars 4 (n = 63), 2 (n = 12) and 5 (n = 10) were characterised, P CR fragments were generated from the beta-lactamase A (blaA) and B (blaB) g enes; in addition, beta-lactamase induction tests were performed with imipe nem as the inducer and beta-lactamase inhibition assays were undertaken wit h aztreonam and clavulanic acid. All the strains yielded PCR amplication fr agments with primers to blaA and blaB. Biovar 4 strains had uniform pattern s of beta-lactamase induction and inhibition: uninduced biovar 4 strains pr edominantly expressed BlaA, but low-level expression of BlaB was also detec ted; after induction, biovar 4 strains predominantly produced BlaB, beta-La ctamase expression varied between and within biovars 2 and 5: uninduced str ains predominantly expressed either BlaA or BlaB, or exclusively BlaB; afte r induction BlaB was predominantly or exclusively expressed. Both the basal and induced levels of beta-lactamase varied within biovars 2 and 5, Some b iovar 5 strains were not inducible; these predominantly produced BlaA, The results of this study show that biovar 2, 4 and 5 strains contain both blaA and blaB, but that the expression of the enzymes is regulated differently between the biovars, and varies within biovars 2 and 5, There was some corr elation between antibiogrtam and the clusters defined from the beta-lactama se induction and inhibition tests, but it was not possible to predict beta- lactamase expression profiles from MIC data.