RESUMEN
Twenty five isolates of S. typhimurium from clinical specimens were studied for markers of virulence. Three of five isolates from blood, both isolates from CSF and urine and only two of fifteen isolates from faeces were positive for fluid accumulation in rabbit ileal loop. All these strains produced an enterotoxic principle, antigenically related to cholera coli family of enterotoxins, as detected by latex agglutination and immuno-dot-blot tests. Polymyxin-B treated 6 h cultures yielded the best toxin. All 5 blood isolates, both CSF isolates and one of the two urine isolates showed low LD50 indicating high virulence. The study thus revealed that some strains of S. typhimurium are more virulent and produce more enterotoxins. These strains invade the intestinal mucosa potently and lead to extra-intestinal manifestations. The low virulent strains, on the other hand, are confined to the intestine and cause mild/moderate gastroenteritis. Enzyme assays were done in 5 representative strains of good, moderate and low toxin producers. Catalase and superoxide dismutase assays did not show any correlation with toxin production, thus suggesting that the enzyme production is unlikely to be a reliable indicator of the virulence for S. typhimurium.