title: Characterization of integron mediated antimicrobial resistance in Salmonella isolated from diseased swine.
abstract: Forty-two Salmonella isolates obtained from diseased swine were genetically characterized for the presence of specific antimicrobial resistance mechanisms. Twenty of these isolates were characterized as S. Typhimurium DT104 strains. Pulsed-field gel electrophoresis was used to determine genetic relatedness and revealed 20 distinct genetic patterns among the 42 isolates. However, all DT104 isolates fell within 2 closely related genetic clusters. Other Salmonella isolates were genetically grouped together according to serotype. All DT104 isolates displayed the penta-resistance phenotype to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline. Resistance to sulfamethoxazole, tetracycline, streptomycin, kanamycin, and ampicillin was most common among the non-DT104 Salmonella isolates. All DT104 strains contained 2 chromosomal integrons of 1000 and 1200 base pairs. The DNA sequencing revealed that the 2 integrons contained genes encoding a resistance to streptomycin and ampicillin, respectively. None of the non-DT104 strains showed the same pattern, although several strains possessed integrons of 1000 base pairs or larger. However, the majority of non-DT104 Salmonella strains did not possess any integrons. Two Salmonella isolates displayed tolerance to the organic solvent cyclohexane, indicating the possibility that they are overexpressing chromosomal regulatory genes marA or soxS or the associated multidrug efflux pump, acrAB. This research suggests that integrons contribute to antimicrobial resistance among specific swine Salmonella serotypes; however, they are not as widely disseminated among non-Typhimurium swine Salmonella serotypes as previously thought.
authors.affiliation: Center for Veterinary Medicine, U.S. Food and Drug Administration, Office of Research, 8401 Muirkirk Road, Laurel, Maryland, USA 20708. dwhite@cvm.fda.gov
authors.forename: David G
authors.initials: DG
authors.lastname: White
authors.forename: Shaohua
authors.initials: S
authors.lastname: Zhao
authors.forename: Patrick F
authors.initials: PF
authors.lastname: McDermott
authors.forename: Sherry
authors.initials: S
authors.lastname: Ayers
authors.forename: Sharon
authors.initials: S
authors.lastname: Friedman
authors.forename: Julie
authors.initials: J
authors.lastname: Sherwood
authors.forename: Missy
authors.initials: M
authors.lastname: Breider-Foley
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Nolan
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000737:chemistry / Q000302:isolation & purification; D024881:Drug Resistance, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field / Q000662:veterinary; D032023:Integrons / Q000502:physiology*; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012475:Salmonella / Q000145:classification / Q000187:drug effects* / Q000235:genetics; D012481:Salmonella Infections, Animal / Q000188:drug therapy / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D012703:Serotyping / Q000662:veterinary; D013552:Swine; D013553:Swine Diseases / Q000188:drug therapy / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial