Development of Biological Intervention Strategies to Reduce Foodborne Pathogen Load in Food Animals

NON-TECHNICAL SUMMARY: Contamination of meat with foodborne pathogens usually results from the carcass coming in contact with the feces of an infected animal during processing. The overall goal of this project is to develop safe, biological methods that effectively reduce foodborne pathogen loads in food animals prior to processing, thereby reducing the likelihood of contamination during processing.<P>APPROACH: <BR>1. Food Safety Vaccine Development. We hypothesize that foodborne pathogen loads in food animals can be reduced using a multi-valent vaccine that simultaneously targets several important bacterial adhesins. The vaccine will be generated and delivered using defective herpesvirus (equine) particles (DHP) as vectors using a protocol well established in our laboratory. If vaccination produces a potentially protective immune response (as measured by mucosal and systemic antibody production), we will then challenge vaccinated animals with each of the targeted bacteria (Salmonella, E. coli, and Listeria). Ultimately, the efficacy of the vaccine will be based upon whether it can significantly reduce the frequency of pathogen shedding. As such, experiments will focus not only on whether early vaccination can limit on-farm shedding rates but whether the vaccine prevents new infections once animals are introduced to typically contaminated environments such as transport crates or holding pens. While the system as it stands presently is designed to vaccinate against Salmonella, E. coli, and Listeria, in the future it will be of interest to expand the spectrum of the vaccine to include other important foodborne pathogens or couple it to other already widely used mucosal vaccines (e.g., infectious bronchitis or infectious bursal disease in poultry, illeitis in pigs) making the vaccine more practical and affordable. <BR>2. Phage Therapy. We hypothesize that pre-transport inoculation of pigs and chickens with concentrated Salmonella-specific phages can significantly reduce new infections in this critical period thereby decreasing the likelihood of contamination during processing. The phage strain(s) used for treatments will be chosen from ten in-hand isolates (obtained from Salmonella-infected pigs) based on growth kinetics, ease of manipulation, and ability to lyse the challenge Salmonella strain. The efficacy of the treatment will be based upon whether new infections and shedding are inhibited or otherwise limited when phage-treated animals are co-mingled with Salmonella-challenged ("seeder") pigs in a Salmonella-contaminated environment. While these experiments utilize Salmonella-specific phages, they are designed to show that the use of phages to combat transport-associated increases in Salmonella infections is an effective use of phage therapy. Once established, it will be of interest to develop the intervention strategy into one that not only targets specific strains of Salmonella but more general Salmonella strains as well as other bacterial species often implicated in foodborne illness outbreaks. <P>
PROGRESS: 2006/10 TO 2007/09
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OUTPUTS: The overall goal of this project is to develop safe, biological methods that effectively reduce foodborne pathogen loads in food animals thereby reducing the likelihood of contamination during processing. Significant progress has been made in specific aim number two: the development of short-term, post-farm bacteriophage therapy designed to counteract rapid infections from contaminated transport crates or trailers and abattoir holding pens. We have isolated several wild-type anti-Salmonella bacteriophage from local wastewater treatment plants. These phage have been characterized phenotypically and genetically and have proven to be highly lytic for Salmonella Typhimurium in the laboratory. We have developed an anti-Salmonella treatment using a cocktail of these phage and have tested the therapy in market weight swine. Surprisingly, after two replications, the treatment has not proved successful in limiting Salmonella infections associated with transportation/lairage. We are currently refining the therapy to make it more effective. Progress has also been made in specific aim number one: the development of a multi-valent mucosal "food safety" vaccine aimed at limiting both on-farm and post-farm colonization rates of foodborne pathogens in poultry and swine. We have successfully produced chimeric plasmids expressing both defective interfering particle genes (vaccine delivery vehicle) and bacterial genes (antigens) in eukaryotic cells. These are essential precursors to producing the actual vaccine. We hope to initially test the immunogenicity of the vaccine in chickens within the coming year. <BR>PARTICIPANTS: Bacteriophage project funded by the National Pork Board. <BR>TARGET AUDIENCES: Pork producers, meat processors. <P>IMPACT: 2006/10 TO 2007/09

<BR>Numerous on-farm strategies exist to limit the foodborne pathogen load (e.g., Salmonella, E. coli, etc.) in food animals. Upon leaving the farm, however, animals are often transported in trailers and held in holding pens that are contaminated with various pathogens. Our work is designed to limit post-farm infections by developing therapies that prevent these new infections. Reductions in the concentrations of foodborne pathogens entering the processing facility will translate to a reduced likelihood of those pathogens contaminating meat.