title: Subtype analysis of Salmonella isolated from subclinically infected dairy cattle and dairy farm environments reveals the presence of both human- and bovine-associated subtypes.
abstract: While it is well established that clinically ill livestock represent a reservoir of Salmonella, the importance of subclinical shedders as sources of human salmonellosis is less well defined. The aims of this study were to assess the subtype diversity of Salmonella in healthy dairy cattle and farm environments and to compare the subtypes isolated from these sources with the Salmonella subtypes associated with clinical human cases in the same geographic area. A total of 1349 Salmonella isolates from subclinical dairy cattle and farm environments (46 farms) were initially characterized by traditional or molecular serotyping and tested for antimicrobial susceptibility. A set of 381 representative isolates was selected for further characterization by pulsed-field gel electrophoresis (PFGE); these isolates represented unique combinations of sampling date, serovar, antimicrobial resistance pattern, farm of origin, and source, to avoid overrepresentation of subtypes that were re-isolated from a given source. These 381 isolates represented 26 Salmonella serovars; the most common serovars were Cerro [(38.8%, 148/381) isolated from 21 farms], Kentucky [16.3%; 10 farms], Typhimurium [9.4%; 7 farms], Newport [7.6%; 8 farms], and Anatum [6.3%; 6 farms]. Among the 381 isolates, 90 (23.6%) were resistant to between 1 and 11 antimicrobial agents, representing 50 different antimicrobial resistance patterns. Overall, 61 XbaI-PFGE types were detected among these 381 isolates, indicating considerable Salmonella diversity on dairy farms. Fourteen PFGE types, representing 12 serovars, exactly matched PFGE types from human isolates, suggesting that subclinically infected dairy cattle could be sources of human disease-associated Salmonella.
authors.affiliation: Department of Food Science, Cornell University, Ithaca, NY 14853, United States.
authors.forename: L D
authors.initials: LD
authors.lastname: Rodriguez-Rivera
authors.affiliation: Department of Food Science, Cornell University, Ithaca, NY 14853, United States.
authors.forename: E M
authors.initials: EM
authors.lastname: Wright
authors.affiliation: Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY 14853, United States.
authors.forename: J D
authors.initials: JD
authors.lastname: Siler
authors.affiliation: Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY 14853, United States.
authors.forename: M
authors.initials: M
authors.lastname: Elton
authors.affiliation: Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY 14853, United States; Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX 77843-4458, United States.
authors.forename: K J
authors.initials: KJ
authors.lastname: Cummings
authors.affiliation: Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, NY 14853, United States.
authors.forename: L D
authors.initials: LD
authors.lastname: Warnick
authors.affiliation: Department of Food Science, Cornell University, Ithaca, NY 14853, United States. Electronic address: mw16@cornell.edu.
authors.forename: M
authors.initials: M
authors.lastname: Wiedmann
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D044822:Biodiversity; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology*; D003612:Dairying; D016521:Electrophoresis, Gel, Pulsed-Field; D004783:Environmental Microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D009518:New York; D010802:Phylogeny; D012475:Salmonella / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D012480:Salmonella Infections / Q000382:microbiology*; D012703:Serotyping
chemical_list: D000900:Anti-Bacterial Agents
keywords: Cattle; Dairy; PFGE; Salmonella; Subclinical; Subtyping