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Applied and Environmental Microbiology, March 2009, p. 1478-1486, Vol. 75, No. 6
0099-2240/09/$08.00+0 doi:10.1128/AEM.01632-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Longitudinal Study of Salmonella Dispersion and the Role of Environmental Contamination in Commercial Swine Production Systems
Paul M. Dorr,1
Daniel A. Tadesse,2
Bayleyegn Molla Zewde,2
Pamela Fry,2
Siddhartha Thakur,3 and
Wondwossen A. Gebreyes2*
Research and Development, Merial Limited, Duluth, Georgia,1 Department of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, Columbus, Ohio,2 Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina3
Received 16 July 2008/ Accepted 24 December 2008
This study investigated the roles of various environmental sources, such as truck-washing systems, waste-processing lagoons, and other sources, as potential contributors to the exposure and dissemination of Salmonella in commercial swine production systems. Four cohorts of nursery age swine herds which originated from distinct farm flows were selected. In addition, cross-sectional sampling of four truck wash stations selected based on the types of disinfectants and sources of water used for sanitizing trucks were tested. Salmonella isolates were recovered from pigs (feces, cecal contents, and mesenteric lymph nodes) and environmental sources (barn floor, lagoon, barn flush, trucks, and holding pens). Antimicrobial susceptibility testing and genotyping were conducted using Kirby-Bauer disk diffusion and amplified fragment length polymorphism, respectively. Salmonella prevalence significantly increased with age from late nursery to slaughter for all of the cohorts (P = 0.007). In two of three instances, all three pig holding pens (lairage) sampled at processing were Salmonella positive. The predominant antibiotypes for all sources included ACSSuT (51.8%), SSuT (16.8%), T (6%), and pansusceptible (7.4%). For the isolates obtained at the farms, the ACSSuT phenotype was 5.6 times more likely to be found in the animals than in the environment (95% confidence interval, 4.4 to 7.2 times). Serogroup B was the most common serogroup (79%), followed by serogroup E (10.4%). Despite the fact that the four production flows were independent, 1 of the 11 genotypic clusters (cluster A1) was commonly detected in any type of sample regardless of its origin. Five of the genotypic clusters (clusters A3, A4, A5, A6, and A7) contained isolates that originated from trucks and lairage swabs and also from cecal contents and/or mesenteric lymph nodes. More interestingly, genotypic clusters A3, A4, and A6 (but not clusters A5 and A7) were not detected on the farms. They originated from the trucks and lairage swabs and then were identified from the cecal contents and/or mesenteric lymph nodes. These findings underscore the significance of various environmental factors, including inadequate truck-washing systems, and emphasize the role of lairage contamination by Salmonella that has food safety significance.
* Corresponding author. Mailing address: Department of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, 1920 Coffey Rd., Columbus, OH 43210. Phone: (614) 292-9559. Fax: (614) 292-4142. E-mail: gebreyes.1{at}osu.edu
Published ahead of print on 9 January 2009.
Applied and Environmental Microbiology, March 2009, p. 1478-1486, Vol. 75, No. 6
0099-2240/09/$08.00+0 doi:10.1128/AEM.01632-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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