Vaccinal properties of Salmonella abortusovis mutants for streptomycin: screening with an ovine model.

Abstract

Living attenuated vaccines may help control infection with Salmonella enterica subspecies enterica ser abortusovis in sheep without constraints incompatible with husbandry. Virulence and immunogenicity of 2 Abortusovis streptomycin-dependent strains and 3 reverse mutants were compared in sheep, the virulent parental strain Abortusovis 15/5 being used as reference. Reduction of virulence with conservation of some immunogenicity was demonstrated for the 5 mutant strains after intravenous or subcutaneous inoculation. A 5-day bacteriemia was detectable after intravenous inoculation with parental strain, whereas none was shown with mutant strains. Mutant reverse strains survived in loco-regional lymph nodes for at least 12 days. The dependent strain D5 and reverse strain Rv6 were selected for subcutaneous vaccination of 2 groups of 18 ewes 32 days before fecundation. Ten pregnant ewes per group and 10 unvaccinated ewes were randomly selected among pregnant animals and were challenged subcutaneously at mid-gestation. Both vaccines conferred protection, but Rv6 was more efficient than D5 and was chosen as the vaccinal strain.