beta-lactamase expression in Yersinia enterocolitica biovars 1A, 1B and 3

Characteristic patterns of beta-lactam susceptibility are associated with d ifferent biovars of Yersinia enterocolitica, In a previous study difference s in beta-lactam susceptibility among biovar 2, 4 and 5 strains were largel y attributed to differences in expression of beta-lactamase A (BlaA) and be ta-lactamase B (BlaB). The basis for differences in beta-lactam susceptibil ity of strains of biovars iii, 1B and 3 is now considered. All the strains examined had blaB; nine of 31 biovar 3 strains and two of 13 biovar 1B stra ins had blaA, but PCR did not amplify blaA from biovar 1A strains. Neverthe less, inhibition data indicated that the majority of uninduced biovar 1A st rains expressed BLaA and BlaB in similar amounts. Strong inducibility was s een in all these strains. Biovar 1B strains (which were less inducible than strains of biovar iii) predominantly produced BlaA without induction; tica rcillin-sensitive strains of biovar 3 produced only BlaB but were not induc ible; without induction biovar 3 strains resistant to ticarcillin and amoxy cillin/clavulanate produced either predominantly BlaA, predominantly BlaB o r exclusively BlaB and induction was demonstrated except for strains produc ing BlaB alone; biovar 3 strains resistant to ticarcillin but sensitive to amosycillin/clavulanate predominantly produced BlaA without induction and w ere inducible for beta-lactamase activity. After induction, nearly all stra ins predominantly or exclusively produced BlaB. Although PCR amplification fragments with primers specific for blaA were obtained only from some strai ns, the induction and inhibition data suggest that all I: enterocolitica st rains possess enzymes related to BlaA- as well as BlaB, Nevertheless, expre ssion of the beta-lactamase is regulated differently in different biovars a nd varies within most biovars. Failure to predict beta-lactamase expression profiles from MIC data indicates the presence of additional mechanisms con tributing to differences in susceptibility.