Evaluation of <i style="">aro</i>A deletion mutant of <i style="">Salmonella enterica</i> subspecies <i style="">enterica</i> serovar Abortusequi for its vaccine candidate potential

Abstract

The present study on a defined deletion <i style="">aro</i>A mutant (B-26) of <i style="">Salmonella enterica </i>subspecies <i style="">enterica </i>serovar Abortusequi (<i style="">S</i>. Abortusequi) for residual virulence and safety in experimental model revealed that the virulence of the strain was at no difference in any of the cell assays (caprine alveolar macrophages, bovine alveolar macrophages, guinea pig blood mononuclear cells and horse blood mononuclear cells) than that of its parent virulence plasmid cured (S-787) and wild type (E-156) strains. The mutant did not cause any apparent illness in baby guinea pigs (15 days old), adult male and female guinea pigs and also not in pregnant (54-55 days of gestation) guinea pigs through oral (4.2 × 10⁹ cfu/ animal) and intramuscular (im) routes (4.2 × 10⁷ cfu/ animal). In pregnant females the mutant also induced abortion as its parent (E-156) though to lesser extent (33%) than the parent strain (100%) on inoculation through intravaginal (4.2 × 10⁹ cfu/ animal) and intraperitoneal (4.2 × 10⁷ cfu/ animal) routes. The babies born from mutant inoculated mothers survived better and were also resistant to intraperitoneal lethal challenge (7.82 × 10⁹ cfu/ animal) with 100% protection. Female guinea pigs challenged after 135-165 days of inoculation with the mutant afforded 100% protection from abortion and mortality caused by lethal infection (7.82 × 10⁹ cfu/ animal) of wild type <i style="">S</i>. <i style="">enterica</i> Abortusequi (E-156). The study revealed that <i style="">aro</i>A mutant (B-26) was safe through oral and im routes for immunization and afforded 100% protection against salmonellosis for more than 5.5 months in guinea pigs. Although immunization with <i style="">aro</i>A mutant in experimental model afforded good protection against abortion and mortality induced by <i style="">S</i>. Abortusequi, further studies are needed in horses to exploit the strain’s vaccine potential in the natural host.