Molecular Characteristics of "BlaB-Like" Chromosomal Inducible Cephalosporinase of Yersinia enterocolitica Biotype 1A Strains.

Yersinia enterocolitica biotype 1A strains are emerging pathogens, frequently isolated from clinical samples across the globe. Y. enterocolitica strains produce two chromosomal ß-lactamases, BlaA and BlaB. BlaA is a constitutively expressed, Ambler class A, penicillinase, whereas BlaB is Ambler class C-type, inducible cephalosporinase. An earlier study from our laboratory indicated that instead of BlaB, Y. enterocolitica biotype 1A produced a "BlaB-like" enzyme. The objective of this work was to study the molecular characteristics of "Bla-B like" ß-lactamases produced by biotype 1A strains to discern their similarity with AmpC-type ß-lactamases and the basis of varied levels of minimum inhibitory concentration (MIC) to cefotaxime. Thus, the promoters and blaB genes were investigated in four strains of biotype 1A. Three-dimensional structures of the "BlaB-like" enzymes were modeled, and docked in silico with cefotaxime to understand how specific substitutions in gene sequences affect antibiotic susceptibilities. Our results indicated that all the reported key catalytic residues were present in variants of "Bla-B-like" enzymes, discerned in biotype 1A strains, but at different positions. Molecular docking of enzyme variants with cefotaxime revealed that lesser was the number of the H-binding residues with cefotaxime in a strain, lower was the MIC of cefotaxime in that strain. To the best of our knowledge, this is the first study in which the molecular characteristics and enzymatic interactions of "BlaB-like" cephalosporinases of Y. enterocolitica biotype 1A strains have been reported.