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JAC Advance Access originally published online on July 21, 2004
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Journal of Antimicrobial Chemotherapy 2004 54(2):401-405; doi:10.1093/jac/dkh365
JAC vol.54 no.2 © The British Society for Antimicrobial Chemotherapy 2004; all rights reserved.

Detection and assay of ß-lactamases in clinical and non-clinical strains of Yersinia enterocolitica biovar 1A

Sachin Sharma, Priya Ramnani and J. S. Virdi*

Microbial Pathogenicity Laboratory, Department of Microbiology, University of Delhi South Campus, Benito Juarez Road, New Delhi—110 021, India

* Corresponding author. Tel: +91-11-26879950; Fax: +91-11-26885270; Email: virdi_dusc{at}rediffmail.com

Objectives: To detect ß-lactamases (A & B) and extended-spectrum ß-lactamases (ESBLs) in clinical and non-clinical isolates of Yersinia enterocolitica biovar 1A, and to determine their activity in the presence of specific lactamase inhibitors.

Methods: The presence of ß-lactamases and ESBLs was detected by disc diffusion in 219 (36 clinical, 183 non-clinical) isolates. ß-Lactamase activity was assayed spectrophotometrically in all 36 clinical and 10 representative non-clinical isolates using nitrocefin as the substrate. Inhibition of ß-lactamases was studied by clavulanic acid, aztreonam and cloxacillin.

Results: Of the 219 isolates, all except two non-clinical isolates indicated the presence of ß-lactamase A (Bla-A) based on the smaller (2–8 mm) radius of the inhibition zone around the ticarcillin disc. Synergy between ticarcillin and co-amoxiclav discs was, however, observed in only 34% of isolates of non-clinical origin. ß-Lactamase B (Bla-B) was found to be consistently positive among all the clinical and non-clinical isolates, as indicated by its characteristic appearance of flattening of the zone of inhibition around the cefotaxime disc adjacent to an imipenem disc. Bla-B was induced more strongly in clinical than in non-clinical isolates. Inhibition of enzyme A by clavulanic acid, aztreonam and cloxacillin was found to be similar, whereas enzyme B was inhibited more strongly by aztreonam and cloxacillin. None of the isolates showed the unequivocal presence of ESBL.

Conclusion: This is the first report on ß-lactamases of Yersinia enterocolitica biovar 1A from Asia. Y. enterocolitica biovar 1A expressed both Bla-A and Bla-B. Heterogeneity was, however, discerned in the expression of Bla-A and by induction of Bla-B among clinical and non-clinical isolates of Y. enterocolitica biovar 1A.

Keywords: constitutive Bla-A , inducible Bla-B , nitrocefin , synergy


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