The beta-lactamases and beta-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 beta-lactam antibiotics and expression of intracellular beta-lactamases. The reasons for the specificity of patterns of susceptibility to beta-lactams for each biotype or subtype of Y. enterocolitica were elucidated by examining their ss-lactamase activity. Whilst the biotypes and subtypes were uniformly susceptible to the newer beta-lactam antibiotics, the susceptibility pattern observed with other beta-lactams was specific to each biotype or subtype, because of the characteristics of beta-lactamase expression by strains within these groups. The susceptibility to these beta-lactam agents depended entirely on the extent of elaboration or the absence of one of the two beta-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 O:5,27 from those of biotype 2, serotype O:9 and biotype 3, serotypes O:1, 2a-3, O:3 and O:5.

The detection of enzyme A of Yersinia enterocolitica by a disc diffusion method.

Yersinia enterocolitica has been described as expressing two types of chromosomal beta-lactamase, the broad spectrum enzyme A and the inducible cephalosporinase enzyme B. Nevertheless, not all Y. enterocolitica strains express both enzyme A and enzyme B; Y. enterocolitica strains of the less commonly isolated biotype 2, serotype O:5 (27) lack the enzyme A. Also, no other members of the Enterobacteriaceae have been demonstrated to produce enzyme A. Detection of this enzyme could therefore be a useful laboratory tool in distinguishing common pathogenic strains of Y. enterocolitica from other Enterobacteriaceae. A simple test by disc diffusion on agar for the recognition of enzyme A expression in Y. enterocolitica was evaluated. The test was based on the resistance to ticarcillin conferred by enzyme A and the highly effective inhibition of this enzyme by clavulanic acid. A typical additional zone of inhibition between the zones of inhibition around a ticarcillin 75 micrograms disc and an amoxycillin/clavulanate 3 micrograms disc was indicative of the presence of enzyme A. By contrast, a large zone of inhibition around the ticarcillin disc without an additional zone of inhibition, reflected the absence of enzyme A.

Characterisation of atypical biotype 3, serotype O:3 Yersinia and development of a simple identification scheme.

Five clinical strains of Yersinia isolated in Japan and identified as atypical biotype 3 or biotype 3B, serotype O:3, phage type II (3*/O:3/II) Yersinia enterocolitica were characterised since the biochemical reactions of these strains indicate they might also belong to the species Yersinia bercovieri. Biochemical tests, characterisation of the beta-lactamases and DNA-DNA hybridization studies provided strong evidence indicating that these strains should be classified as Yersinia enterocolitica. A simple scheme combining a disc diffusion test and four biochemical tests was devised for identification of these atypical strains.

Susceptibility to beta-lactam agents of Yersinia enterocolitica biotype 4, serotype O3 isolated in various parts of the world.

Forty-eight human isolates of Yersinia enterocolitica of biotype 4, serotype O3 from various parts of the world were examined for susceptibility to 13 beta-lactam agents. The intracellular beta-lactamases of each of the 48 strains were examined. Isolates from Europe, Asia and Brazil (phage type VIII) or South Africa and Hungary (phage type IXa) produced both enzyme A and enzyme B, whereas isolates from New Zealand and Australia (phage type IXb) lacked the cephalosporinase enzyme B. Among the seven strains isolated in Canada belonging to phage type IXb, three strains expressed only enzyme A (group I) whereas the other four strains produced both enzymes A and B (group II). The high susceptibility to the combination of amoxycillin and clavulanate observed in one subtype was explained by the absence of the cephalosporinase enzyme B. A simple disk diffusion test with this antibiotic combination was shown to be effective in the detection of enzyme B in Y. enterocolitica 4/O3.

The prevalence of inducible beta-lactamase in clinical isolates of Yersinia enterocolitica.

In a prevalence study, 100 clinical isolates of Yersinia enterocolitica belonging to biotypes 1A, 3 and 4 isolated in Australia were examined for the induction of beta-lactamase in broth at 28 degrees C using imipenem as an inducer. An increase in beta-lactamase activity ranging from 15 to 93 fold was observed with all 36 isolates of biotypes 1A and 3 confirming that both enzyme B and enzyme "B-like" in biotype 3 and biotype 1A Yersinia enterocolitica were readily inducible. By contrast, imipenem failed to induce beta-lactamase in any of the 64 isolates of Yersinia enterocolitica belonging to biotype 4.

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.

Biotype and antibiotic sensitivity of 100 clinical isolates of Yersinia enterocolitica.

One hundred clinical isolates of Yersinia enterocolitica were biotyped, serotyped and tested for in-vitro sensitivity to seven beta-lactam antibiotics and six other antibiotics. Twenty-four of the isolates belonged to Niléhn's and Wauters' biotype 1A, 12 to biotype 3 and 64 to biotype 4. No biotypes 1B or 2 strains were found. All isolates were sensitive to chloramphenicol, ciprofloxacin, gentamicin, tetracycline, trimethoprim and all but one to sulphafurazole. All were resistant to ampicillin with MIC's ranging from 32 to 256 mg/L, but were susceptible to ticarcillin/clavulanic acid and imipenem. With other beta-lactam agents there were different patterns of sensitivity, specific to each of the three biotypes. All biotype 4 strains were resistant to carbenicillin and ticarcillin but sensitive to amoxycillin/clavulanic acid and cefoxitin. Biotype 3 strains, by contrast, were sensitive to carbenicillin and ticarcillin but resistant to amoxycillin/clavulanic acid and cefoxitin, whilst biotype 1A strains were resistant to each of these four beta-lactam agents.

A study of the beta-lactamases of 100 clinical isolates of Yersinia enterocolitica.

The intracellular beta-lactamases of 100 distinct clinical isolates of Yersinia enterocolitica were examined, to investigate the effect of selected beta-lactam agents on the enzymes. The enzyme inhibition profiles obtained were specific to each of the three biotypes 1A, 3 and 4. Biotype 4 strains elaborated only one beta-lactamase with a pI of 8.3 corresponding to the carbenicillin-hydrolysing beta-lactamase enzyme A of Cornelis & Abraham. Biotype 3 strains also produced a single beta-lactamase with a pI of 5.4-5.6 corresponding to enzyme B, the chromosomally mediated inducible cephalosporinase. Two beta-lactamases were found in biotype 1A strains, one was identical to enzyme A and the other, although showing a slight difference in pI to enzyme B, was similar to this enzyme in other respects. The differences in the distribution of enzyme A and enzyme B in strains of Y. enterocolitica belonging to the biotypes 1A, 3 and 4 isolated in Australia, explain the different patterns of susceptibility to beta-lactam antibiotics.

Mutation of Pseudomonas aeruginosa to piperacillin resistance mediated by beta-lactamase production.

Piperacillin-resistant mutants were detected in each of ten strains of Pseudomonas aeruginosa. The resistance was associated with constitutive production by the strains of high levels of beta-lactamase which was similar in character to the induced chromosomal Id beta-lactamase of the parent strains. This type of mutation to piperacillin-resistance occurred at a low frequency. The beta-lactamase production and piperacillin-resistance were stable on repeated subculture and prolonged storage of the strains.