title: Change in antimicrobial resistance pattern in Salmonella enterica serovar Typhimurium isolates detected in a beef cattle farm.
abstract: Multidrug-resistant Salmonella enterica serovar Typhimurium (S. Typhimurium) isolates with four different antimicrobial resistance patterns obtained from a beef cattle farm were characterized to determine their clonality. Macrorestriction analysis of genomic DNA revealed that these four isolates are closely related to each other and can be classified as a newly emerged pulsed-field gel electrophoresis type among cattle: cluster VII. Three of the four isolates showed resistance to extended-spectrum cephalosporins (ESCs), and this resistance was mediated by AmpC β-lactamase encoded by the bla(CMY-2) gene in a 190-kbp IncA/C plasmid. Results of restriction analysis and IncA/C backbone PCR suggest that the three 190-kbp plasmids are identical and that a 70-kbp IncA/C plasmid of the ESC-susceptible isolate is derived from the 190-kbp plasmid by a deletion event. Three isolates harboured a virulence-resistance plasmid (165 or 180 kbp), and restriction analysis revealed that these plasmids were identical or closely related to each other. These results suggest that the four S. Typhimurium cluster VII isolates originate from a common ancestor that probably invaded the farm prior to the salmonellosis outbreak. Antimicrobial resistance patterns may not necessarily reflect the relationships of the isolates.
authors.affiliation: Aizu Livestock Hygiene Service Center, Aizuwakamatsu, Fukushima, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Sugawara
authors.forename: Francis
authors.initials: F
authors.lastname: Shahada
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Izumiya
authors.forename: Haruo
authors.initials: H
authors.lastname: Watanabe
authors.forename: Ikuo
authors.initials: I
authors.lastname: Uchida
authors.forename: Yukino
authors.initials: Y
authors.lastname: Tamamura
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kusumoto
authors.forename: Taketoshi
authors.initials: T
authors.lastname: Iwata
authors.forename: Masato
authors.initials: M
authors.lastname: Akiba
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology*; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial; D016680:Genome, Bacterial; D012481:Salmonella Infections, Animal / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial