Control of Salmonella in Infected Chickens by Combining Application of Bacteriophages, Competitive Exclusion, and Maternal Immunity

NON-TECHNICAL SUMMARY: Paratyphoid Salmonella continue to be one of the largest causes of food-borne illness in the U.S. Poultry meat and eggs are a major source of Salmonella food-borne illness. With the growing concern over the use of antibiotics in food animals, new approaches to reducing Salmonella in poultry are needed. The purpose of this project is to combine two traditional approaches to Salmonella reduction with a novel third approach to significantly further reduce Salmonella in poultry.

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APPROACH: New bacteriophages will be isolated and characterized for their lytic activity against Salmonella in vitro and their Salmonella-reducing activity in vitro. Bacteriophage mixtures alone and in combination with competitive exclusion and/or maternal passive immunity will be administered to chickens experimentally infected with Salmonella. Assessment of protection will be based on Salmonella isolation from ceca and spleen using quantitative bacteriology and fluorescence resonance energy transfer real time PCR. The quantity of Salmonella in treated and control birds, and the percentages of positive/negative birds in each group, will be measured and compared by appropriate statistical methods. Treatments that show promise in reducing Salmonella numbers in the laboratory will be tested in larger scale experiments using mass application of the treatment(s) using facilities in which chickens will be exposed to stressors that are found in broiler production facilities. The efficacy of the treatments will be evaluated both at pre-harvest and harvest using an experimental processing plant.

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PROGRESS: 2007/09 TO 2008/09<BR>

OUTPUTS: Objective 1, Develop mixtures of distinct bacteriophages that show lytic activity against Salmonella. In Year 2 of the project, 4 lytic phages (S2a, S4, S9, and S13) previously examined by killing curves were further analyzed in vitro. Using a liquid lysis approach, it was shown that all 4 phage lysed exponentially growing cultures of Salmonella Typhimurium beginning 3-4 h after inoculation with 104 - 105 pfu/ml. <BR>
Objective 2, Evaluate the efficacy of combining phages, competitive exclusion, and maternal passive antibody for reducing Salmonella colonization in experimentally infected chickens. In Year 1, the optimal Salmonella Typhimurium dose for infecting >80% of the chicks was determined. In Year 2, optimization of phage treatments was initiated. One group of chicks was phage treated one time post-Salmonella challenge, while another group of chicks was phage-treated once pre-challenge and daily post-challenge. Control chicks received Salmonella challenge but no phage treatment. At intervals post-challenge, cloacal and cecal cultures were performed for Salmonella enumeration. Cultures from ceca and cloaca showed that phage treatment reduced Salmonella numbers up to 5 days post-challenge, compared to cultures from non-treated control chicks. However, Salmonella numbers in ceca and cloaca of treated chicks no longer showed a treatment effect by 7 days post-challenge. <BR>
PARTICIPANTS: Combined personnel from co-investigators Price, McKee, and Toro's labs worked on the cloacal sampling, cecum excision, and bacteriologic culture of the chicks. The Toro lab personnel trained personnel from the Dept. of Poultry Science, Auburn University, to perform chick inoculations, cloacal culture, and chick necropsy and cecum removal. The McKee lab personnel trained other project personnel on the use of an automated agar plate inoculater, and on the use of an automated plate counter. <BR>
TARGET AUDIENCES: Poultry production veterinarians and scientists interested in pre-harvest food safety would be a target audience for our preliminary results showing reduction of Salmonella following bacteriophage treatment. <P>
IMPACT: 2007/09 TO 2008/09<BR>
The goal of the project is to incorporate bacteriophage treatment of chickens with traditional intervention methods to augment Salmonella reduction. Year 2 results showed that bacteriophage treatment is effective for 5 days, after which no treatment effect is apparent. Thus, in broiler poultry production, bacteriophage treatment should be targeted in the first few days of life to thwart Salmonella colonization, and then during the last few days before slaughter, to reduce Salmonella numbers in the feces, resulting in less carcass contamination by this pathogen.