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Appl. Environ. Microbiol., 06 1997, 2372-2377, Vol 63, No. 6
JL Pace, TJ Chai, HA Rossi and X Jiang
Many enteric pathogens are thought to enter a viable but nonculturable
state when deprived of nutrients. Virulent strains of the enteric pathogen
Vibrio parahaemolyticus are rarely isolated from their low- nutrient
aquatic environments, possibly due to their nonculturability. Host factors
such as bile may trigger release from dormancy and increase virulence 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 virulent strains. This
effect was not demonstrated in the nonvirulent strains, and it was reversed
by extraction of bile acids with cholestyramine. Bile-treated V.
parahaemolyticus had lower levels of intracellular calcium than untreated
cells, and this effect coincided with an increase in the number of
metabolically active cells. Chelation of intracellular calcium with
BAPTA/AM (R. Y. Tsien, Biochemistry 19:2396-2402, 1980) produced similar
results. Addition of bile to V. parahaemolyticus cultures in laboratory
medium enhanced factors associated with virulence such as Congo red
binding, bacterial capsule size, and adherence to epithelial cells. These
results suggest that a bile acid-containing environment such as that found
in the human host favors growth of virulent 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.
Copyright © 1997, American Society for Microbiology
Effect of bile on Vibrio parahaemolyticus
Horn Point Environmental Laboratory, University of Maryland, Cambridge, USA.
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