title: Transposons related to Tn1696 in IncHI2 plasmids in multiply antibiotic resistant Salmonella enterica serovar Typhimurium from Australian animals.
abstract: Conjugative IncHI2 plasmids carrying tetracycline, trimethoprim, and sulphonamide resistance genes were recovered from two multiply antibiotic resistant Salmonella enterica serovar Typhimurium isolates from Australian food-producing animals. Transposons related to the mercury resistance transposon Tn1696 were identified in both IncHI2 plasmids. These transposons contained an In4-type class 1 integron that carried a dfrA5 trimethoprim resistance gene cassette and the sul1 sulfonamide resistance gene. These integrons were located in the same position as In4 in Tn1696. The integron from one isolate includes a large transposon-like structure containing four IS26 and the strAB, sul2, bla(TEM), and aphA1 genes conferring resistance to streptomycin, sulphonamides, ampicillin, kanamycin, and neomycin, respectively. This structure is flanked by an 8-bp duplication, but it includes both the aphA1-containing transposon Tn4352 and a transposon, Tn6029, carrying genes derived from RSF1010 and from Tn2. However, Tn4352 and Tn6029 overlap, sharing one IS26 copy. This suggests that they do not move by a standard transpositional mechanism. A circular intermediate, carrying only the region containing the resistance gene(s) and one of the IS26 bounding it, is proposed as an intermediate.
authors.affiliation: School of Molecular Bioscience, The University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Amy K
authors.initials: AK
authors.lastname: Cain
authors.forename: Xiulan
authors.initials: X
authors.lastname: Liu
authors.forename: Steven P
authors.initials: SP
authors.lastname: Djordjevic
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Hall
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001315:Australia / Q000453:epidemiology; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000382:microbiology*; D004251:DNA Transposable Elements / Q000235:genetics*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D032023:Integrons / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics*; D012481:Salmonella Infections, Animal / Q000453:epidemiology* / Q000382:microbiology; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D017422:Sequence Analysis, DNA
chemical_list: D000900:Anti-Bacterial Agents; D004251:DNA Transposable Elements