USE OF VACCINE AND BIOLOGICAL-CONTROL TECHNIQUES TO CONTROL PATHOGENS IN ANIMALS USED FOR FOOD

An important component of a Hazard Analysis Critical Control Point (HACCP) approach applied to animal production is reducing the carriage of food-associated pathogens by animals. Two approaches that have both great potential for reducing pathogen colonization of animals and merit for practical application include (1) vaccination and (2) competitive exclusion. Vaccination involves acquisition of immunity in an animal following exposure to an attenuated pathogen or an antigen of a virulent microorganism. Adherence factors that influence bacterial colonization of animals are useful antigens for vaccines. A strategy to developing a vaccine to reduce carriage of pathogens includes (I) identifying sites of colonization by the pathogen in the animal, (2) defining the mechanism of colonization, (3) characterizing genes that encode colonization factors, (4) transforming the colonization factor antigen genes into a suitable nonpathogenic vector, and (5) determining the optimal methods of immunization. Studies are underway to identify colonization factors of Escherichia coli O157:H7 for use in vaccine development to protect cattle from colonization by this pathogen. Competitive exclusion involves the use of microbial cultures that out-compete pathogens from colonizing specific niches. A science-based approach to identifying/developing useful competitive exclusion cultures is to: (1) define how a pathogen colonizes the site of interest, (2) isolate microbes that colonize the same site and produce metabolites that inhibit or kill the pathogen, and (3) verify that the inhibitory microbes, when introduced into pathogen-free animals, can reduce or prevent colonization by the pathogen. This approach has been used successfully to identify defined bacterial cultures that can greatly reduce colonization of Campylobacter jejuni in poultry. Commercial implementation of techniques of these types is an essential part of the overall HACCP approach to reducing the prevalence of foodborne pathogens from farm to fork.