Yersinia enterocolitica O:3. Antimicrobial resistance patterns, virulence profiles and plasmids.

Antimicrobial resistance patterns (ARP), virulence profiles and plasmids in clinical isolates of Yersinia enterocolitica serotype O:3 were studied. The ARP was tested using the disk method. All strains were susceptible to amoxicillin/clavulanic acid, cefoxitin, fosfomycin, gentamicin, kanamycin, neomycin, tetracycline, nalidixic acid, norfloxacin, ciprofloxacin and trimethoprim. All of them presented resistance to ampicillin, all with the exception of one to cephalotin, differing in resistance or susceptibility to chloramphenicol, streptomycin (Sm), sulfadiazine (Sd) and cotrimoxazole. Due to these differences they were grouped into 8 ARP. Twenty-nine strains carried plasmids and were grouped into 5 plasmid profiles. All strains carrying 42 MDa plasmids were positive for virulence tests (calcium dependence, crystal violet binding, Congo red binding and autoagglutination). No correlation between ARP and plasmid profile was found, although small plasmids of 6.5 and 4.1 MDa mediated resistance to Sm-Sd, as was shown by transformation to Escherichia coli strains. DNAs from plasmids were analyzed by restriction enzymes. All 42 MDa plasmids showed identical EcoRI and HindIII profiles. The two 6.5 MDa plasmids showed identical BglII, AvaI and SalI restriction profiles and the four 4.1 Mda plasmids also yielded restriction profiles similar to each other, but different from the 6.5 ones.