B-469. Osmotic and Acid Tolerance Responses in Vibrio parahaemolyticus: Pre-Adaptation in High NaCl Cross Protects in Low pH

W. B. Whitaker, L. M. Naughton, E. F. Boyd;
Univ. of Delaware, Newark, DE.

Vibrio parahaemolyticus is halophilic and an inhabitant of marine coastal environments. V. parahaemolyticus is a pathogen of humans, the leading cause of seafood-associated bacterial gastroenteritis. Thus, the bacterium has to respond to different stress conditions such as osmotic fluctuations in the external environment and acidic conditions in the human stomach. Salinity is an absolute requirement for growth and V. parahaemolyticus can grow in up to 10% NaCl. The mechanisms of osmotolerance in V. parahaemolyticus are unknown as is the role it plays in cross protection to acid stress. We identified on chromosome 1 of V. parahaemolyticus RIMD2210633, a putative ectoine synthesis system and Betaine Choline Carnitine transporter (BCCT) clustered next to a ProU transporter. Also on chromosome 1 are an OpuD and a second BCCT transporter. On chromosome 2, a putative betaine synthesis system is clustered with a second ProU transporter, and a BCCT and PutP transporter are also present. This is double the number of compatible solute systems found in other Vibrio and the most among Proteobacteria. We performed comparative physiological analysis of V. parahaemolyticus to V. vulnificus, V. cholerae and V. fischeri grown under varying NaCl concentrations and temperatures. We show that in all cases V. parahaemolyticus had a growth advantage and that this unique compendium of systems enhances V. parahaemolyticus ability to grow at high salinity. We constructed knockout mutants of the unique osmotolerance cluster on chromosome 1 in V. parahaemolyticus RIMD2210633 by allelic exchange. We demonstrate that these mutations display growth defects at high salt concentration. Next, we determined whether growth at high NaCl concentrations cross protected at low pH. When pre-adapted at low NaCl concentrations, V. parahaemolyticus could not grow at mild pH 5 but pre-adaptation at high NaCl allowed grow in pH 5. We also show that V. parahaemolyticus pre-adapted in 3% NaCl increased the survival rate of at pH 4. Growth at high NaCl may give V. parahaemolyticus a competitive advantage in vivo, thus an important virulence mechanism, which is now under investigation

163/B. Secretion Systems of Pathogenic Microorganisms - I

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