ANTIBIOTIC-RESISTANCE OF AGRICULTURAL AND FOODBORNE SALMONELLA ISOLATES IN CANADA - 1986-1989

A total of 689 Salmonella cultures isolated during 1986-1989 from Canadian agricultural products and from imported fish, shellfish, and reptiles were examined for resistance to a test panel of 11 antibiotics. The incidence of antibiotic resistance in strains from all sources seemingly increased during the study period, whereas the occurrence of resistance within individual sample categories fluctuated annually. Although poultry figured as a major reservoir of resistant salmonellae (53.4%), red meats and fish/shellfish also yielded substantial numbers of resistant strains. The range of streptomycin (27.1 to 48.7%) and tetracycline (24.3 to 37.8%) resistance among poultry and red meat isolates, and identification of meat isolates carrying chloramphenicol (0.4 to 9.1%) and ampicillin (3.4 to 11.4%) resistance codons was disquieting. Most of the multiply-resistant (greater-than-or-equal-to 2 antibiotics) strains belonged to somatic serogroups B and C, with poultry occurring as the principal reservoir of multiresistant phenotypes. Of the 27 resistance patterns encountered in this study, all but two contained a resistance determinant for streptomycin and/or tetracycline. These findings underscore a disturbing level of antibiotic resistant Salmonella in the food chain, and the need to reassess the alleged benefits of subtherapeutically medicated feeds in current animal husbandry practices.