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.