Characterization of small ColE1-like plasmids conferring kanamycin resistance in Salmonellaenterica subsp. enterica serovars Typhimurium and Newport

Multi-antibiotic resistant (MR) Salmonella enterica serovars Typhimurium and Newport are an increasing concern in human and animal health. Many strains are known to carry antibiotic resistance determinants on multiple plasmids, yet detailed information has been scarce. Three plasmids conferring kanamycin (Kan) resistance were isolated and nucleotide sequences were determined. Two KanR plasmids from Salmonella Newport strains, pSN11/00Kan and pSN02/01Kan, were found to be identical and were 5698 bp in size. Plasmid pG7601Kan from Salmonella Typhimurium phage type U302 strain G7601 was 3208 bp, and was the same as the previously reported pU302S from another U302 strain G8430. All three plasmids carried identical aph(3′)-I genes. The plasmids were ColE1-like, containing RNA I/RNA II and the rom gene. Plasmids pSN11/00Kan and pSN02/01Kan also carried mobilization genes mobC and mobABD, similar to those of the pColK-K235 and pColD-157 plasmids from the colicinogenic Escherichia coli strains. All three plasmids were stable without kanamycin selection for ∼100 generations.