Evaluation of vaccine candidate potential of ΔaroA, ΔhtrA and ΔaroAΔhtrA mutants of Salmonella enterica subspecies enterica serovar Abortusequi in guinea pigs.

Salmonella enterica subspecies enterica serovar Abortusequi (S. Abortusequi), a host adapted Salmonella causes abortions, still births and foal mortality in equids. Though known since more than 100 years, it is still a problem in many of the developing countries including India. There is dearth of really good vaccine affording immunity lasting at least for one full gestation. In search of a potential vaccine candidate, three defined deletion mutants (ΔaroA, ΔhtrA and ΔaroAΔhtrA) of S. Abortusequi were tested in guinea pig model for attenuation, safety, immunogenicity, humoral immune response, protective efficacy and persistence in host. The ΔhtrA and ΔaroAΔhtrA mutants were found to be safe on oral inoculation in doses as high as 4.2×109 cfu/animal. Also through subcutaneous inoculation ΔaroAΔhtrA mutant did not induce any abortion in pregnant guinea pigs. All the three mutants did not induce any illness or death in 1-2 week-old baby guinea pigs except ΔhtrA mutant which caused mortality on intraperitoneal inoculation. Inoculation with mutants protected against challenge and increased breeding efficiency of guinea pigs. After >4.5 months of mutant inoculation, guinea pigs were protected against abortifacient dose of wild type S. Abortusequi and mother guinea pigs also conferred resistance to their babies to the similar challenge. Early humoral immune response of S. Abortusequi mutants was characteristic. Faecal excretion of ΔaroA and htrA mutants was detected up to 45 days of inoculation in guinea pigs while ΔaroAΔhtrA mutant could not be detected after 21 days of inoculation. The results indicated that the double deletion mutant (ΔaroAΔhtrA) was the most effective and safe candidate for vaccination against S. Abortusequi through mucosal route of inoculation.

Effect of Salmonella typhimurium toxin on the expression of rabbit intestinal functions.

BACKGROUND & OBJECTIVES: Infection by Salmonella Typhimurium is one of the leading causes of intestinal dysfunction, however the underlying mechanism of this effect is largely unknown. Hence the effect of enterotoxin secreted by Salmonella Typhimurium-(S-LT) was studied on D-glucose absorption and brush border enzymes in rabbit ileum. mRNA levels encoding these proteins were also analysed. METHODS: Adult male New Zealand white rabbits were used. The polymyxine B extract of enterotoxin obtained from Salmonella Typhimurium was tested for the presence of enterotoxicity by rabbit ileal loop test. D-glucose uptake by ileal tissue was measured by the tissue accumulation method. Intestinal brush border membranes were isolated and the effect of S-LT on various brush border enzymes studied. RESULTS: S-LT significantly inhibited (P < 0.01) the absorption of Na+ dependent D-glucose uptake but had no effect on Na+ independent sugar uptake in rabbit ileum. The activities of brush border sucrase (72% P < 0.001) and lactase (47% P < 0.01) and alkaline phosphatase (43% P < 0.01) were also significantly reduced in infected animals as compared to the controls. Northern blot analysis revealed that mRNA levels encoding Na+ glucose co-transporter (SGLT1), brush border lactase and sucrase activities were unaffected in Salmonella infected rabbit ileal loops. INTERPRETATION & CONCLUSION: The findings suggest that the intestinal dysfunctions observed in Salmonella infection are unrelated to mRNA expression encoding Na+ glucose co-transporter and brush border enzyme proteins in rabbit ileum.