Drug resistance among pathogenic bacteria from animals in Ontario.

Prevalence of antimicrobial drug resistance among over 3000 clinical isolates of animal pathogens in Ontario during 1971-72 has been studied. A high number of multiple resistance patterns is prevalent among members of Enterobacteriaceae, especially Escherichia coli and Salmonella typhimurium. The most common resistance pattern among bovine strains was against not less than six drugs in common use. Among different animal species the bovine population was found to be the source of a high percentage of chloramphenicol resistant E. coli and S. typhimurium organisms. All the isolates resistant to this drug were in addition resistant to three or more other antibiotics of established therapeutic value. All the multiple resistant isolates of S. typhimurium tested had R factors and they transferred most of the resistance determinants including that for chloramphenicol to a recipient E. coli in vitro.Penicillin resistance among Staphylococcus aureus of bovine mammary origin did not appear to be high. Antimicrobial drug susceptibility patterns of staphylococci, streptococci and Corynebacterium sp indicate effective in vitro activity with many antimicrobial agents.