ANTIMICROBIAL SUSCEPTIBILITY OF PATHOGENIC YERSINIA-ENTEROCOLITICA ISOLATED IN CANADA FROM 1972 TO 1990

Yersinia enterocolitica has emerged as an enteropathogen associated wi th several types of human infections that often require antimicrobial therapy, but little is, known about the antimicrobial susceptibilities of pathogenic strains isolated from humans in Canada. To determine th e present patterns of antimicrobial susceptibility, to identify change s in these patterns that occurred during the past two decades, and to investigate the relationships between O serotypes and patterns of susc eptibility, we tested a total of 1,105 pathogenic Y. enterocolitica st rains isolated during 1972 to 1976, 1980, 1985, and 1990 for their sus ceptibilities to 22 antimicrobial agents. Susceptibility testing was p erformed by using a single breakpoint concentration in agar procedure. The results showed that all strains were susceptible to ciprofloxacin and piperacillin, and 98% or more of the strains from each period wer e susceptible to trimethoprim, sulfamethoxazole, cotrimoxazole, tetrac ycline, chloramphenicol, cefamandole, cefotaxime, aztreonam, and four aminoglycosides. In contrast, all strains were nonsusceptible to eryth romycin, furazolidone, and clindamycin and 90% or more of the strains from each period were nonsusceptible to ampicillin, carbenicillin, tic arcillin, and cephalothin. Strains belonging to serotypes O:3, O:5,27, and O:8 had different patterns of susceptibility to ampicillin, carbe nicillin, ticarcillin, and amoxicillin-clavulanic acid. No major diffe rence in susceptibility was observed between any of the groups of huma n or animal strains included in the study, but nonsusceptibility to te tracycline increased from 0.4% in 1985 to 2% in 1990 in human strains isolated in those years. Our results indicate that between 1972 and 19 90 there was no marked decrease in susceptibility to agents commonly u sed for therapy among pathogenic Y. enterocolitica strains isolated in Canada.