Beta-lactamase induction by imipenem in Yersinia enterocolitica

Five strains of Yersinia enterocolitica belonging to 5 different biotypes were induced to beta-lactamase production with imipenem in broth culture at 28 degrees C. Strains belonging to biotypes 1A, 1B, 2 and 3 showed a 26 to 73 fold increase in beta-lactamase activity after 180 min in the presence of 0.5 mg/L imipenem. Biotype 4 strain, by contrast, did not show obvious enhancement of its beta-lactamase activity in the same experiments. Enzyme B in biotypes 1B, 2 and 3 and enzyme "B-like" in biotype 1A were shown to be responsible for the increase of the beta-lactamase activity, but neither enzyme nor any similar enzyme was found to be present in biotype 4 strain.