AEM Accepts, published online ahead of print on 23 October 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.00785-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Phage therapy to reduce pre-processing Salmonella infections in market weight swine

Samantha K. Wall, Jiayi Zhang, Marcos H. Rostagno, and Paul D. Ebner^*

Department of Animal Sciences, Purdue University, 915 W. State St., West Lafayette, IN 47907; and USDA-ARS, Livestock Behavior Research Unit, West Lafayette, IN 47907

^* To whom correspondence should be addressed. Email: pebner{at}purdue.edu.

Contamination of meat products with foodborne pathogens usually results from the carcass coming in contact with the feces of an infected animal during processing. In the case of Salmonella, pigs can become colonized with the organism during transport and lairage from contaminated trailers and holding pens resulting in increased pathogen shedding just prior to processing. Increased shedding, in turn, amplifies the likelihood of carcass contamination by magnifying the amount of bacteria that enters the processing facility. We conducted a series of experiments to test whether phage therapy could limit Salmonella infections at this crucial period. In a preliminary experiment done with small pigs (3-4 weeks; 30-40 pounds), administration of an anti-Salmonella phage cocktail at the time of inoculation with Salmonella enterica Typhimurium reduced Salmonella colonization by 99.0-99.9% (2-3 log reduction) in the tonsils, ileum, and cecum. To test the efficacy of phage therapy in a production-like setting, we inoculated four market weight pigs (in three replicates) with Salmonella enterica Typhimurium and allowed the challenged pigs to contaminate a holding pen for 48 hours. Sixteen naïve pigs were randomly split into two groups that received either the anti-Salmonella phage cocktail or a mock-treatment. Both groups of pigs were comingled with the challenged pigs in the contaminated pen. Treatment with the anti-Salmonella phages significantly reduced cecal Salmonella concentrations (95%, P < .05) while also reducing (numerically) ileal Salmonella concentrations (90%, P = .06). Additional in vitro studies showed that the phage cocktail was also lytic against several non-Typhimurium serovars.