Relationships between beta-lactamase production and beta-lactam susceptibility of environmental strains of Yersinia kristensenii.

Strains of Yersinia kristensenii display high susceptibility to carbenicillin (MIC90 less than 8 micrograms/ml) in comparison with the majority of environmental strains of Yersinia closely related to Y. enterocolitica which are resistant to this antibiotic (MIC90 greater than 256 micrograms/ml). beta-lactamases of 39 strains of Y. kristensenii isolated from foods were analysed by isoelectric focusing and gel electrophoresis of ultrasonically disrupted uninduced cultures. beta-lactamase patterns showed the presence of only one out of three classes of enzymes of pI 6.7, 7.6 and 8.2, respectively, by strain. One beta-lactamase showed electrophoretic mobility different (EM + 2.0 cm/h) from that of all the other enzymes (EM + 1.6 cm/h) belonging to the class of pI 7.6. Induction by cefoxitin revealed the existence of inducible beta-lactamases in two out of eight selected strains. The substrate profile of these enzymes, which are probably chromosomally mediated, showed a predominant cephalosporinase activity. None of the type A and B beta-lactamases described by Cornelis and Abraham in Y. enterocolitica were found in any of the strains examined. The lack of beta-lactamase A (a penicillinase) accounts for the carbenicillin susceptibility of Y. kristensenii strains.