B-263. Salmonella enterica serovar Typhimurium Succinate Dehydrogenase/Fumarate Reductase Double Mutant is Avirulent and Immunogenic in BALB/c Mice

R. Mercado-Lubo¹, E. J. Gauger², M. P. Leatham¹, T. Conway³, P. S. Cohen¹;
¹Univ. of Rhode Island, Kingston, RI, ²Intervet Inc., Millsboro, DE, ³Univ. of Oklahoma, Norman, OK.

In a previous study, it was shown that that the TCA cycle operates as a full cycle during Salmonella enterica serovar Typhimurium SR-11 per-oral infection of BALB/c mice. The evidence was that a ΔsucCD mutant (succinyl-CoA synthetase), which prevents the conversion of succinyl-CoA to succinate and an ΔsdhCDA mutant (succinate dehydrogenase), which blocks the conversion of succinate to fumarate, were both attenuated, whereas an SR-11 ΔaspA mutant (aspartase) and an SR-11 ΔfrdABCD mutant (fumarate reductase), deficient in the ability to run the reductive branch of the TCA cycle, were fully virulent. In the present study, evidence is presented that a serovar Typhimurium SR-11 ΔfrdABCD ΔsdhCDA double mutant is avirulent in BALB/c mice and protective against subsequent infection with the virulent serovar Typhimurium SR-11 wildtype strain via the per-oral route and highly attenuated via the intraperitoneal route. These results suggest that fumarate reductase, which normally runs in the opposite direction to succinate dehydrogenase, can replace it during infection by running in the same direction as succinate dehydrogenase to run a full TCA cycle in an SR-11 ΔsdhCDA mutant. The data also suggest that conversion of succinate to fumarate plays a key role in serovar Typhimurium virulence. Moreover, the data raise the possibility that S. enterica ΔfrdABCD ΔsdhCDA double mutants and ΔfrdABCD ΔsdhCDA double mutants of other intracellular bacterial pathogens with complete TCA cycles may prove to be effective live vaccine strains for animals and humans.