Salmonella-Free Broilers by Live Vaccine-Induced Innate Resistance to Colonisation and Invasion and Novel Methods to Eliminate Vaccine and Field Strains

Salmonella in broiler poultry remains the major source of infection for man and is the least tractable because of the young age at which broilers are slaughtered and their immunological immaturity. Previously we have found that intestinal colonisation of newly-hatched chicks with live, attenuated Salmonella vaccine strains results in the development of a rapid and profound resistance to intestinal infection (from a specific microbiological exclusion mechanism) and also to tissue invasion (from an induction of heterophil infiltration into the intestine).<P>
We will exploit these phenomena by screening strains of Salmonella serotypes Typhimurium, Enteritidis and Hadar for these phenotypes, introducing attenuating mutations and assessing their protective effect in broilers under experimental and simulated field conditions. The degree of attenuation induced and the host cell responses to the vaccines will also be studied. <P>
In addition, we will explore the potential of new biotechnological approaches for the elimination of pathogenic bacteria (wild-type and vaccine strains) from the chicken intestine by a) identifying colonisation genes in Salmonella and mutating them, b) exploring the potential of introducing inducible bacterial suicide genes into Salmonella, c) studying host defensin production in the intestine and its induction by vaccines, d) dietary manipulation to modulate expression of invasion genes.
Microarray technology will be used to identify colonisation and heterophil-induction genes and examine host responses. <P> We will also exploit our expertise in phage technology to explore the use of bacteriophages to control intestinal infection and reduce carcass contamination by Salmonella and Campylobacter and use these in association with vaccine strains to test a combined approach to pathogen elimination.