DRUG-RESISTANCE, PLASMIDS, BIOTYPES AND SUSCEPTIBILITY TO BACTERIOPHAGES OF SALMONELLA ISOLATED FROM POULTRY IN CANADA

Salmonella isolates from 295 layer and 294 broiler flocks in Canada we re examined to determine resistance to antimicrobial agents, plasmid p rofiles, biochemical properties, and susceptibility to polyvalent bact eriophages. Except for the high number of strains resistant to spectin omycin (97.8%), the frequency of drug resistance of Salmonella isolate s from layer flocks was low. None of 457 isolates from layer flocks wa s resistant to amikacin or ciprofloxacin, and less than 2% of the stra ins were resistant to cephalothin, chloramphenicol, cotrimoxazole, gen tamicin, kanamycin, neomycin, nitrofurantoin, and/or polymyxin B. Abou t 3% of the Strains were resistant to ampicillin, carbenicillin and/or tetracycline, whereas 8% of the strains were resistant td sulfisoxazo le, Salmonella anatum var. O15 + and S. typhimurium var. Copenhagen st rains were resistant to multiple antimicrobial agents. None of 1159 Sa lmonella strains from broiler flocks was resistant tb amikacin, cephal othin, ciprofloxacin or polymyxin B, less than 1% of the strains were resistant to chloramphenicol 2% were resistant to ampicillin, carbenic illin and/or chloramphenicol; 5-7% were resistant to the aminoglycosid es gentamicin, kanamycin and/or neomycin; 6% were resistant to nitrofu rantoin; 10% to tetracycline; 14% to sulfisoxazole; and 99% to spectin omycin. A high percentage of S. binza, S. anatum var. O15 +, S. schwar zengrund and S. heidelberg stains were resistant to antimicrobial agen ts. Some of the single or multiple resistances were encoded by conjuga tive plasmids or by plasmids that were thermosensitive for transfer. E ight percent of S. heidelberg strains did not produce hydrogen sulfide . Ninety-seven percent of the Salmonella strains were susceptible to t he lytic effect of polyvalent bacteriophages.