Distribution of beta-lactamases A and B in some groups of Yersinia enterocolitica and their role in resistance.

Yersinia enterocolitica W222 (serological group 3) synthesized two different intracellular beta-lactamases, called A and B. Enzyme B was more sensitive than A to inhibition by cloxacillin. The minimum inhibitory concentrations of various beta-lactam antibiotics for strains of Y. enterocolitica of groups 3 and 9 and the effect of cloxacillin on these concentrations suggested differential roles for beta-lactamases of types A anb B in penicillin and cephalosporin resistance. Type B enzymes protected Y. enterocolitica against cephalothin and cephalosporin C, wheras type A enzymes protected very efficiently against carbenicillin. Protection against other beta-lactam antibiotics was exerted by both enzymes. However, while both enzymes readily hydrolysed cephaloridine and showed no crypticity with this substrate, they only conferred a very weak protection against it. This may be because cephaloridine reached its target quickly, before it was degraded. The resistance of strains of Y. enterocolitica from groups I, 2 and I6 was also explicable in terms of a two-enzyme system, whereas strains belonging to group 5b produced only a type B lactamase and were sensitive to carbenicillin.