Biochemical and genetic characterization of the beta-lactamases of Y. aldovae, Y. bercovieri, Y. frederiksenii and "Y. ruckeri" strains.

The beta-lactamases of five strains each of Y. aldovae and "Y. ruckeri", and 10 strains each of Y. bercovieri and Y. frederiksenii were examined phenotypically and genetically. Beta-lactamase activity and induction assays and SDS-PAGE were applied for phenotypic characterization of these enzymes. Genotypically, PCR experiments applying degenerated primer pairs for the detection of AmpC beta-lactamase genes were performed. All yersiniae yielded specific amplification products for ampC and all these strains expressed beta-lactamases. Each species produced its own, species-specific AmpC beta-lactamase. Inducibility of these enzymes was shown for Y. bercovieri, but not for the low-level enzyme producing species Y. aldovae and "Y. ruckeri". In contrast to these species, induction tests for Y. frederiksenii revealed heterogeneous results. Whereas the beta-lactamases of 6 of 10 strains were inducible, the enzyme activities after induction in the remaining four were similar to those measured without an inducer. In addition to the AmpC enzyme, all Y. frederiksenii strains expressed a second beta-lactamase belonging to Ambler class A. The present study enlarges the knowledge about the beta-lactamases of four novel Yersinia species that are likely to be involved in human disease. Beta-lactamases of Y. aldovae and "Y. ruckeri" have been characterized for the first time.