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

An important component of a Hazard Analysis Critical Control Point (HA CCP) approach applied to animal production is reducing the carriage of food-associated pathogens by animals. Two approaches that have both g reat 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 virule nt microorganism. Adherence factors that influence bacterial colonizat ion of animals are useful antigens for vaccines. A strategy to develop ing 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 colon ization factors, (4) transforming the colonization factor antigen gene s into a suitable nonpathogenic vector, and (5) determining the optima l methods of immunization. Studies are underway to identify colonizati on factors of Escherichia coli O157:H7 for use in vaccine development to protect cattle from colonization by this pathogen. Competitive excl usion involves the use of microbial cultures that out-compete pathogen s from colonizing specific niches. A science-based approach to identif ying/developing useful competitive exclusion cultures is to: (1) defin e how a pathogen colonizes the site of interest, (2) isolate microbes that colonize the same site and produce metabolites that inhibit or ki ll the pathogen, and (3) verify that the inhibitory microbes, when int roduced 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 Ca mpylobacter 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.