Evaluation of Protective Efficacy of Live Attenuated Salmonella enterica Serovar Gallinarum Vaccine Strains against Fowl Typhoid in Chickens

Abstract

ABSTRACTSalmonella entericaserovar Gallinarum is the etiological agent of fowl typhoid, which constitutes a considerable economic problem for poultry growers in developing countries. The vaccination of chickens seems to be the most effective strategy to control the disease in those areas. We constructedS. Gallinarum strains with a deletion of the global regulatory genefurand evaluated their virulence and protective efficacy in Rhode Island Red chicks and Brown Leghorn layers. Thefurdeletion mutant was avirulent and, when delivered orally to chicks, elicited excellent protection against lethalS. Gallinarum challenge. It was not as effective when given orally to older birds, although it was highly immunogenic when delivered by intramuscular injection. We also examined the effect of apmimutant and a combination offurdeletions with mutations in thepmiandrfaHgenes, which affect O-antigen synthesis, andansB, whose product inhibits host T-cell responses. TheS. Gallinarum Δpmimutant was only partially attenuated, and the ΔansBmutant was fully virulent. The ΔfurΔpmiand ΔfurΔansBdouble mutants were attenuated but not protective when delivered orally to the chicks. However, a ΔpmiΔfurstrain was highly immunogenic when administered intramuscularly. All together, our results show that thefurgene is essential for the virulence ofS. Gallinarum, and thefurmutant is effective as a live recombinant vaccine against fowl typhoid.