Evaluation of aroA deletion mutant of Salmonella enterica subspecies enterica serovar Abortusequi for its vaccine candidate potential.

The present study on a defined deletion aroA mutant (B-26) of Salmonella enterica subspecies enterica serovar Abortusequi (S. 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 x 10(9) cfu/ animal) and intramuscular (im) routes (4.2 x 10(7) 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 x 10(9) cfu/ animal) and intraperitoneal (4.2 x 10(7) cfu/ animal) routes. The babies born from mutant inoculated mothers survived better and were also resistant to intraperitoneal lethal challenge (7.82 x 10(9) 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 x 10(9) cfu/ animal) of wild type S. enterica Abortusequi (E-156). The study revealed that aroA 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 aroA mutant in experimental model afforded good protection against abortion and mortality induced by S. Abortusequi, further studies are needed in horses to exploit the strain's vaccine potential in the natural host.

Evaluation of guinea pig model for experimental Salmonella serovar Abortusequi infection in reference to infertility.

The present study conclusively revealed the role for Salmonella enterica subspecies enterica serovar Abortusequi in conception failure. None of the 12 guinea pigs conceived when orally exposed to sublethal dose of the pathogen during breeding, while 66.67% of animals in control group were found pregnant during same period of observation under similar conditions. Salmonella carrier animals also had drastic reduction in conception rate (16.67%). During mid pregnancy, S. Abortusequi exposure to guinea pigs through intravaginal, intramuscular and subcutaneous routes induced fetal death followed by resorption. While 2 out of 6 orally inoculated and 3 out of 6 intraperitonially inoculated guinea pigs aborted, in rest of the animals fetal death was followed by meceration and resorption. It was interesting to note that S. Abortusequi could not persist longer than a week in males while in pregnant females it could be detected for >10 weeks after inoculation. In late pregnancy, most of the exposed animals aborted and non aborting animals though had normal parturition, survival rate of their babies was nearly zero in comparison to the control group. The study revealed role for S. Abortusequi in impairing conception, abortion, early fetal deaths, fetal meceration and resorption. Further studies are required to identify factors responsible for increased susceptibility of females particularly during pregnancy.