SURVEY OF PLASMIDS AND RESISTANCE FACTORS AMONG VETERINARY ISOLATES OF SALMONELLA-ENTERITIDIS IN MALAYSIA

Thirty-five veterinary isolates of Salmonella enteritidis were charact erized by their susceptibility to 10 antimicrobial agents and by their plasmid profiles on agarose gel electrophoresis. All were susceptible to carbenicillin, chloramphenicol and nalidixic acid but 89% were res istant to tetracycline. When examined, 91% of the isolates harboured p lasmids, with sizes ranging from 9.8 to 60 MDa. However, it was only p ossible to associate the presence of plasmids with tetracycline resist ance; plasmids occurring in 90% of the tetracycline-resistant isolates . In conjugation experiments, with Escherichia coli K12 Nal(r) as reci pient, the tetracycline resistance in three selected S. enteritidis is olates was observed to transfer at frequencies of 3.0 x 10(-3) to 1.0 x 10(-2)/donor cell. The concomitant transfer of a 56-MDa or 60-MDa pl asmid in these three S. enteritidis isolates was also detected.