The β-lactamases and β-lactam antibiotic susceptibility of Yersinia enterocolitica

One hundred and forty-five isolates of Yersinia enterocolitica of different serotypes and biotypes, including atypical biotypes, collected from various parts of the world, were examined for their susceptibility to β-lactam antibiotics and expression of intracellular β-lactamases. The reasons for the specificity of patterns of susceptibility to β-lactams for each biotype or subtype of Y. enterocoliticawere elucidated by examining their β-lactamase activity. Whilst the biotypes and subtypes were uniformly susceptible to the newer β-lactam antibiotics, the susceptibility pattern observed with other β-lactams was specific to each biotype or subtype, because of the characteristics of β-lactamase expression by strains within these groups. The susceptibility to these β-lactam agents depended entirely on the extent of elaboration or the absence of one of the two β-lactamases, enzyme A and enzyme B, found in the species. Detection of enzyme B by a disc diffusion test yielded inconsistent results, but detection of enzyme A by disc diffusion was highly reliable. This test clearly distinguished strains of biotype 2, serotype 0:5,27 from those of biotype 2, serotype O:9 and biotype 3, serotypes O:1, 2a-3, 0:3 and 0:5.