Background: The presence of β-lactamases in Y. enterocolitica has been reported to vary with serovars, biovars and geographical origin of the isolates. An understanding of the β-lactamases in other related species is important for an overall perception of antibiotic resistance in yersiniae. The objective of this work was to study the characteristics of β-lactamases and their genes in strains of Y. intermedia and Y. frederiksenii, isolated from clinical and non-clinical sources in India. Results: The enzymes, Bla-A (a constitutive class A penicillinase) and Bla-B (an inducible class C cephalosporinase) were found to be present in all the clinical and non-clinical strains of Y. intermedia and Y. frederiksenii by double disc diffusion method. The results showed differential expression of Bla-A as indicated by presence/absence of synergy whereas expression of Bla-B was quite consistent. The presence of these enzymes was also reflected in the high minimum inhibitory concentrations, MIC₅₀ (126–1024 mg/L) and MIC₉₀ (256–1024 mg/L) of β-lactam antibiotics against these species. Restriction fragment length polymorphism (RFLP) revealed heterogeneity in both blaA and blaB genes of Y. intermedia and Y. frederiksenii. The blaA gene of Y. intermedia shared significant sequence identity (87–96%) with blaA of Y. enterocolitica biovars 1A, 1B and 4. The sequence identity of blaA of Y. frederiksenii with these biovars was 77–79%. The sequence identity of blaB gene of Y. intermedia and Y. frederiksenii was more (85%) with that of Y. enterocolitica biovars 1A, 1B and 2 compared to other species viz., Y. bercovieri, Y. aldovae and Y. ruckeri. Isoelectric focusing data further revealed that both Y. intermedia and Y. frederiksenii produced Bla-A (pI 8.7) and "Bla-B like" (pI 5.5–7.1) enzymes. Conclusion: Both Y. intermedia and Y. frederiksenii showed presence of blaA and blaB genes and unequivocal expression of the two β-lactamases. Limited heterogeneity was detected in blaA and blaB genes as judged by PCR-RFLP. Phylogenetic relationships showed that the two species shared a high degree of identity in their bla genes. This is the first study reporting characteristics of β-lactamases and their genes in strains of Y. intermedia and Y. frederiksenii isolated from Asian region.

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