title: Multilocus variable-number tandem-repeat analysis and plasmid profiling to study the occurrence of blaCMY-2 within a pulsed-field gel electrophoresis-defined clade of Salmonella enterica serovar Typhimurium.
abstract: Salmonella enterica serovar Typhimurium circulating in food animal populations and carrying resistance to antimicrobial agents represents a human health risk. Recently, a new clade of S. Typhimurium, WA-TYP035/187, was reported in cattle and humans in the Pacific Northwest, United States of America. The objective of this study was to describe a possible mechanism of acquisition of expanded-spectrum cephalosporin resistance in this clade. Ceftazidime resistance increased steadily among WA-TYP035/187 isolates, from 0% (0/2) in 1999 to 77.8% (28/36) in 2006 (chi2 for linear trend, P value of <0.001). Among 112 bovine-source and 18 human-source isolates, 49 (43.8%) and 12 (66.7%) were resistant to ceftazidime, respectively. Multiple-locus variable-number tandem-repeat analysis (MLVA) and plasmid profiling suggested that resistance was acquired by multiple independent genetic events within the WA-TYP035/187 clade. Given the lack of an obvious reservoir in species other than cattle and a parallel rise in ceftiofur resistance in the bovine-specific serovar Salmonella enterica serovar Dublin in the same time frame and region, selection pressure due to the use of the expanded-spectrum cephalosporin drug ceftiofur in cattle is a likely factor driving the increasing cephalosporin resistance of WA-TYP035/187.
authors.affiliation: AAHP, Field Disease Investigation Unit, Department of Veterinary Clinical Sciences, Washington State University, Pullman, WA 99164, USA.
authors.forename: B
authors.initials: B
authors.lastname: Adhikari
authors.forename: T E
authors.initials: TE
authors.lastname: Besser
authors.forename: J M
authors.initials: JM
authors.lastname: Gay
authors.forename: L K
authors.initials: LK
authors.lastname: Fox
authors.forename: D D
authors.initials: DD
authors.lastname: Hancock
authors.forename: M A
authors.initials: MA
authors.lastname: Davis
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D002417:Cattle; D016000:Cluster Analysis; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D008826:Microbial Sensitivity Tests; D018598:Minisatellite Repeats; D017720:Molecular Epidemiology; D010957:Plasmids / Q000032:analysis*; D012480:Salmonella Infections / Q000382:microbiology*; D012481:Salmonella Infections, Animal / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D014481:United States; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics*; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D047090:beta-Lactams; C103022:beta-lactamase CMY-2; D001618:beta-Lactamases