EFFECT OF BILE ON VIBRIO-PARAHAEMOLYTICUS

Many enteric pathogens are thought to enter a viable but nonculturable state when deprived of nutrients. Virulent strains of the enteric pat hogen Vibrio parahaemolyticus are rarely isolated from their low-nutri ent aquatic environments, possibly due to their nonculturability. Host factors such as bile may trigger release from dormancy and increase v irulence in these strains. In this study, the addition of bile or the bile acid deoxycholic acid to estuarine water-cultured bacteria led to an increase in the direct viable count and colony counts among the vi rulent strains. This effect was not demonstrated in the nonvirulent st rains, and it was reversed by extraction of bile acids with cholestyra mine. Bile-treated V. parahaemolyticus had lower levels of intracellul ar calcium than untreated cells, and this effect coincided with an inc rease in the number of metabolically active cells. Chelation of intrac ellular calcium with BAPTA/AM (R. Y. Tsien, Biochemistry 19:2396-2402, 1980) produced similar results. Addition of bile to V. parahaemolytic us cultures in laboratory medium enhanced factors associated with viru lence such as Congo red binding, bacterial capsule size, and adherence to epithelial cells. These results suggest that a bile acid-containin g environment such as that found in the human host favors growth of vi rulent strains of V. parahaemolyticus and that bile acids enhance the expression of virulence factors. These effects seem to be mediated by a decrease in intracellular calcium.