Growth Characterization of Single and DoubleMethionine Auxotroph Strains for Potential Vaccine Use in Poultry.

Abstract

Poultry meat is an important source of zoonoticinfection. Oral vaccination of chickens with live attenuatedduring grow-out is an attractive approach to controlcolonization in the chicken gastrointestinal tract. In this study, we report the construction of methionine-dependent and growth ofTyphimurium mutant strains with methionine auxotrophy (Δand ΔΔ) and survival in chicken feed and fecal matrices. The methionine auxotroph mutant ΔΔgrew slowly on L-methionine but failed to grow on D-methionine, as expected, and exhibited lower affinity for methionine compared with the isogenic parent strain (Δsingle mutant) in whole-cell affinity experiments. Preliminary data conducted as part of a previously published bird challenge study indicated that the methionine auxotroph was less effective at protection in chickens to a challenge with virulent wild-type parent strain but generated greater-specific serum IgG. Although the auxotroph could not sustain itself in minimal media it was able to survive when incubated in the presence of chicken and fecal material. The immune response appears promising but further work may be needed to alter low-affinity methionine transporters and methionine biosynthesis genes in combination with the knock-out of the high affinity transporterreported here to ensure timely clearance of the candidate vaccine strain.