An in-vitro study of the antimicrobial susceptibilities of Yersinia enterocolitica and the definition of a database

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Abstract
The antibiotic susceptibilities of 151 Yersinia enterocolitica strains isolated from humans, animals and the environment, and belonging to biovars 1A (n = 22), 1B (n = 13), 2 (n = 12), 3 (n = 31), 4 (n = 63) and 5 (n = 10) to 71 antibiotics were examined. Biovars could be characterized phenotypically by their similar antibiograms. For the majority of biovars only minor differences in susceptibilities were detected. Ninety-nine percent of all Yersinia strains were resistant to amoxycillin, but biovar-related differences in MICs were demonstrated. Significant differences, characteristic of specific biovars, were detected for fosfomycin, some β-lactams (in particular amoxycillin/clavulanate, and ticarcillin). Strains of biovar 1A were resistant or of intermediate susceptibility to ticarcillin and had fosfomycin MICs of 16–64 mg/L and amoxycillin/ clavulanate MICs of 4–32 mg/L. Most strains of biovar 1B (n = 11) were sensitive to amoxycillin/clavulanate (MIC = 0.5–2 mg/L). Most strains of biovar 2 (n = 10) showed an antibiotic phenotype resembling that of strains of biovar 1A, but they were more susceptible to fosfomycin (MIC = 4–16 mg/L). Twenty-seven strains of biovar 3 had amoxycillin/clavulanate MICs of 4–32 mg/L; 19 of them were sensitive to ticarcillin and fosfomycin. Biovar 4 strains were uniformly sensitive or of intermediate susceptibility to amoxycillin/clavulanate (MIC = 0.5–4 mg/L), sensitive to fosfomycin (MIC = 1–4 mg/L) but resistant to ticarcillin. The prevailing antibiotic phenotype of biovar 5 (n = 7) was similiar to the phenotype of biovar 4, although these biovar 5 strains were slightly more susceptible to amoxycillin/clavulanate and showed a heterogeneous pattern of susceptibility to fosfomycin (MIC = 1–32 mg/L). The results of this study show that unambiguous statements cannot be made about the natural antibiotic susceptibility to certain β-lactams and fosfomycin of Y. enterocolitica. The data indicate a complex regulation of β -lactamases in Y. enterocolitica. Some β-lactamases are found more frequently or will be expressed predominantly in specific biovars.

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