Purification and characterization of enterotoxic moiety present in cell-free culture supernatant of Salmonella typhimurium

Development and evaluation of gamma irradiated toxoid vaccine of Salmonella enterica var Typhimurium

Development of a single effective vaccine against non-typhoidal salmonellosis is very challenging due to the presence of hundreds of serovars of Salmonella which are antigenically different from each other. The Salmonella enterotoxin (Stn), a common virulence factor occurring amongst a wide range of serovars, used as a formalized toxoid vaccine has been found to be effective against homologous and heterologous serovars. However, the process of formalization has its own drawbacks. Gamma radiation (γ) on the other hand is widely used as a safe and convenient method of sterilization worldwide. In this experiment we used gamma rays to inactivate the partially purified Stn of Salmonella enterica serovar Typhimurium (DT 193). The toxoid obtained was tested for its immunogenicity and loss of toxicity and then used to formulate a gamma irradiated toxoid vaccine (ITST). The efficacy of the developed ITST was tested in Kuroiler, a Broiler breed, against homologous and heterologous challenges (S. Typhimurium and S. Gallinarum) administered intra-peritoneally and orally. Birds in groups challenged with S. Typhimurium by both routes recorded protective indices (PI) of 100% while birds in groups challenged intra-peritoneally with S. Gallinarum recorded PI of 83.33% and those challenged orally scored 100%. The overall protective index (PI) being 95.83%. The antibody titres calculated as geometric mean with standard error at 1:10(-4) dilutions showed a steep rise after the first dose and peaked at week 6 post primary vaccinations. Thus the ITST was found very effective in protecting poultry against both the challenge organisms tested.

Effect of ondansetron on Salmonella typhimurium-induced net fluid accumulation in the pig jejunum in vivo

Two major pathophysiological mechanisms explaining the diarrhoea induced by Salmonella typhimurium have been suggested to be: (a) invasion of the intestine by the bacteria, and (b) an enterotoxin resembling Vibrio cholerae toxin. Cholera toxin is a potent secretagogue in pig small intestine and induces secretion partly by activating 5-hydroxytryptamine receptors, following release of 5-hydroxytryptamine. Ondansetron is a selective 5-hydroxytryptamine-3 receptor antagonist, which reduces the cholera toxin-evoked fluid accumulation in pig jejunum. The aim of this study was to investigate the effect of ondansetron on Salmonella typhimurium-induced fluid accumulation in ligated loops of pig jejunum in vivo. 10(10) colony-forming units of the bacteria was injected into loops and incubated for 8 hr. 200 mg x kg-1 ondansetron given subcutaneously reduced the Salmonella typhimurium-induced fluid accumulation by about 40%. This results suggests the involvement of 5-hydroxytryptamine and 5-hydroxytryptamine-3 receptors in Salmonella typhimurium-induced diarrhoea.

Immunogenicity and antigenic relationship of Salmonella enterotoxin with other enterotoxins

The immunogenicity and antigenic relationship of Salmonella enterotoxin with other enterotoxins were studied. The purified enterotoxin of Salmonella typhimurium strains was immunogenic in rabbits and antiserum produced against it completely neutralized the enterotoxic activity of purified as well as crude enterotoxins. The Salmonella enterotoxin did not cross-react with cholera toxin, heat-labile enterotoxin of Escherichia coli or Shiga toxin. On the other hand, enterotoxins produced by different serotypes of Salmonella were antigenically related. Heat, pH and proteolytic enzymes had not only adversely affected the enterotoxigenicity but also the antigenicity of the Salmonella enterotoxin. However, formalin was found to completely destroy the enterotoxigenicity of enterotoxin without affecting the antigenicity. Formalin-treated enterotoxin may thus be tried as a vaccine to prevent the diarrhoeal syndrome induced by enterotoxigenic salmonellae.

Salmonella enterotoxin (stn) gene is prevalent among strains of Salmonella enterica, but not among Salmonella bongori and other Enterobacteriaceae

All strains and serovars of Salmonella enterica such as serovar Typhimurium, Enteritidis, Dublin, Typhi, etc. were found to carry the Salmonella enterotoxin determinant stn as far as examined in PCR and hybridization studies. However, using MDCK cells for testing the toxicity of the strains under investigation, only a limited number of stn positive strains revealed phenotypically the Salmonella enterotoxin Stn. In contrast to S. enterica, other Enterobacteriaceae including Salmonella bongori were found neither genotypically nor phenotypically Stn toxin positive.