Natural antimicrobial susceptibilities and biochemical profiles of Yersinia enterocolitica-like strains: Y. frederiksenii, Y. intermedia, Y. kristensenii and Y. rohdei.

The natural susceptibility of 131 Yersinia strains of Y. frederiksenii (n=38), Y. intermedia (n=48), Y. kristensenii (n=26) and Y. rohdei (n=19) to 70 antibiotics was tested. Minimum inhibitory concentration (MIC) values were determined with a microdilution procedure in IsoSensitest broth (all strains) and cation-adjusted Mueller Hinton broth (some strains). All species were naturally sensitive or sensitive and of intermediate susceptibility to tetracyclines, aminoglycosides, acylureidopenicillins, numerous cephalosporins, carbapenems, aztreonam, quinolones, chloramphenicol, folate-pathway inhibitors, nitrofurantoin, and fosfomycin. Uniform natural resistance was found with penicillin G, oxacillin, several macrolides, lincosamides, streptogramins, glycopeptides, rifampicin and fusidic acid. Species-specific differences in susceptibility affecting clinical assessment criteria were seen with aminopenicillins (in the presence and absence of beta-lactamase inhibitors), ticarcillin and some cephalosporins. Major medium-dependent susceptibilities were found with fosfomycin. beta-Lactam MIC susceptibility patterns suggested that most strains of the species tested produce both class A and class C (AmpC) beta-lactamases that are characteristic for the species. The present study describes a database concerning the natural susceptibility of some Y. enterocolitica-like species to a wide range of antibiotics, which can be applied to validate forthcoming antibiotic susceptibility tests of these strains and might contribute to their identification. An evaluation of 30 biochemical tests that secured phenotypic identification to the Yersinia species level is presented.