The correlation of biochemical virulence factors and enterotoxin production with LD50 of Salmonella typhimurium in mice.

Five strains of Salmonella typhimurium were examined to determine the parameters of virulence. The virulent species significantly resisted the macrophage bactericidal activity (p less than 0.05). The chemiluminescent (CL) response was studied to determine the level of Oxygen-free radicals (OFR) generated and the antioxidant enzymes superoxidase dismutase (SOD), catalase and glutathione peroxidase were assayed to determine the antioxidant mechanism of S. typhimurium to subvert these microbicidal pathways. The levels of the various enzymes were correlated with the virulence (as determined by LD50) and the ability of the microorganisms to induce diarrhoea. Oxygen free radical (OFR) generation elicited by macrophages, in the presence of virulent and avirulent salmonellae was not statistically significant (p greater than 0.05). No correlation was found between the levels of the antioxidant enzymes and the LD50 values. Thus the oxygen-dependent pathways do not appear to play a role in the pathogenesis of salmonellosis, and do not specify the virulence of the microorganism. Immunological and biological assays revealed the virulent strain to be more toxigenic than the avirulent strain. Therefore, the basis of differing virulence in S. typhimurium may be the ability to make and release more toxin in vivo.