Control of colonization by virulent Salmonella typhimurium by oral immunization of chickens with avirulent Δcya Δcrp S. typhimurium

Oral immunization with a ΔcyaΔcrp Salmonella typhimurium strain has been shown to preclude colonization by wild-type, virulent S. typhimurium and induces humoral and cellular immune response in chickens. Intestinal tract colonization by the virulent challenge strain was used to determine the level of protection conferred by immunization with the Δcya Δcrp mutant. The associated humoral and cellular immune responses were measured by ELISA and delayed-type hypersensitivity (DTH) tests, respectively. The levels of colonization by both Salmonella strains were determined by enumeration of viable cells in the intestinal tract. A reduction in faecal excretion of the wild-type strain was observed with a single oral immunization with the Δcya Δcrp mutant, but caecal colonization was not affected. However, double oral immunization with the Δcya Δcrp mutant precludes caecal colonization by the virulent strain. IgM, IgA and IgG were detected against sonicated Salmonella whole-cell antigens. Outer membrane and flagella proteins induced DTH responses, whereas lipopolysaccharide failed to do so. The effectiveness of the Δcya Δcrp strain in reducing caecal colonization by the highly virulent challenge strain in chickens demonstrates that oral vaccination with the Δcya Δcrp S. typhimurium should aid in eliminating Salmonella carriers in chickens. The elimination of these carriers on the poultry farm should help to cotrol Salmonella contamination of poultry products, thereby improving public health.