Vaccination against Salmonella, enterohaemorrhagic E. coli and Campylobacter in food-producing animals.
The threat of zoonotic infection with food-poisoning enteric pathogens remains a major threat to public health throughout the world. Control of enteric pathogens within food-producing animals remains an obvious strategy to prevent the introduction of these pathogens into the human food chain. Vaccines are currently available for the control of Salmonella; however such vaccines vary in their efficacy and acceptability to the food production industries and consumers. Vaccines for the control of enterohaemorrhagic E. coli and Campylobacter are currently unavailable. Understanding the molecular basis of how these organisms colonize the intestines and cause disease is essential for the development of effective multivalent vaccines. The mechanisms by which these organisms colonize the gut will be reviewed. Bacterial Type Three Secretion Systems (TTSS) have been shown to be major virulence factors influencing the colonization and pathogenicity of Salmonella and enterohaemorrhagic E. coli in some but not all animal species. Thus, understanding the specific nature of host/pathogen interactions is crucial in the development of cross-species vaccines. TTSSs act by delivering effector proteins into intestinal epithelial cells, which act to modify signalling events in host cells causing cytoskeletal and pathophysiological changes to the benefit of the pathogen. Disruption of TTSSs and/or related secreted effector proteins can be adopted as a strategy for the attenuation of live vaccine strains. Furthermore secreted effector proteins have the potential to be incorporated into sub-unit vaccines. As many of such effector proteins are conserved between different serotypes, such vaccines offer the hope of cross-serotype protective immune responses. Novel experimental vaccines are currently being developed to exploit these and other recent discoveries in bacterial virulence mechanisms. The potential of such vaccines to control zoonotic pathogens will be discussed.