Antibiotic susceptibilities of Yersinia enterocolitica and Y. intermedia isolates from aquatic environments.

Of 37 Yersinia isolates from various aquatic environments, seven were Y. enterocolitica and 30 Y. intermedia. These isolates were biotyped, serotyped and tested for their susceptibility to 20 antibiotics. All Y. enterocolitica isolates were of biovar 1; those of Y. intermedia were distributed amongst four biovars (1, 2, 4 and 6). On the basis of combined biotyping and serotyping results, Y. enterocolitica isolates were distributed in five and Y. intermedia in 17 groups. With the exception of one Y. enterocolitica isolate which was resistant to tetracycline and streptomycin, the isolates were sensitive to the non-beta-lactam antibiotics. In contrast, various patterns of beta-lactam insensitivity were detected, including ampicillin and ticarcillin (35 isolates), cephalothin (33 isolates), carbenicillin (32 isolates), amoxycillin/clavulanate (23 isolates) and cefoxitin (22 isolates). No correlation between biotype or serotype and the susceptibility pattern of the isolates was apparent. Both inducible cephalosporinase activity against third-generation cephalosporins and inhibition of resistance to penicillins were detected in all Y. enterocolitica and Y. intermedia isolates by double-disk tests.