Background: Vibrio parahaemolyticus is abundant in the aquatic environment particularly in warmer waters and is the leading cause of seafood borne gastroenteritis worldwide. Prior to 1995, numerous V. parahaemolyticus serogroups were associated with disease, however, in that year an O3:K6 serogroup emerged in Southeast Asia causing large outbreaks and rapid hospitalizations. This new highly virulent strain is now globally disseminated.
Vibrio parahaemolyticus inhabits marine, brackish, and estuarine waters worldwide, where fluctuations in salinity pose a constant challenge to the osmotic stress response of the organism. Vibrio parahaemolyticus is a moderate halophile, having an absolute requirement for salt for survival, and is capable of growth at 1 to 9% NaCl. It is the leading cause of seafood-related bacterial gastroenteritis in the United States and much of Asia. We determined whether growth in differing NaCl concentrations alters the susceptibility of V. parahaemolyticus O3:K6 to other environmental stresses. Vibrio parahaemolyticus was grown at a 1% or 3% NaCl concentration, and the growth and survival of the organism were examined under acid or temperature stress conditions. Growth of V. parahaemolyticus in 3% NaCl versus that in 1% NaCl increased survival under both inorganic (HCl) and organic (acetic acid) acid conditions. In addition, at 42°C and ؊20°C, 1% NaCl had a detrimental effect on growth. The expression of lysine decarboxylase (encoded by cadA), the organism's main acid stress response system, was induced by both NaCl and acid conditions. To begin to address the mechanism of regulation of the stress response, we constructed a knockout mutation in rpoS, which encodes the alternative stress sigma factor, and in toxRS, a two-component regulator common to many Vibrio species. Both mutant strains had significantly reduced survival under acid stress conditions. The effect of V. parahaemolyticus growth in 1% or 3% NaCl was examined using a cytotoxicity assay, and we found that V. parahaemolyticus grown in 1% NaCl was significantly more toxic than that grown in 3% NaCl.Vibrio parahaemolyticus is a Gram-negative bacterium that inhabits coastal waters worldwide. Vibrio parahaemolyticus grows optimally in warmer waters and is most commonly isolated during the summer months, often in association with plankton, crustaceans, mollusks, and fish (16,17). During the winter months, the organism is typically scarce and usually is isolated from sediment samples (16). While V. parahaemolyticus has been shown to be the etiological agent of disease in several kinds of crustaceans and shellfish, it is most notably a pathogen of humans (17). Vibrio parahaemolyticus was first discovered in Japan during an outbreak of gastroenteritis in 1950 (12). It is the leading cause of seafood-related bacterial gastroenteritis in the United States and much of Asia (6,39). Infection is most frequently associated with the consumption of oysters harvested from warm waters, particularly along the U.S. Gulf Coast, where vibrios grow to high levels during the summer months (6, 7, 42). Newly released data from the CDC comparing the incidence rates of laboratory-confirmed infections by gastrointestinal pathogens in 1996 to 2008 revealed an increase of 47% for Vibrio infections, of which V. parahaemolyticus accounted for 55%, while rates for all other enteric pathogens decreased or remained the same (5). An outbreak of V. parahaemolyticus infections which caused rapid hos...
Vibrio parahaemolyticus is a moderately halophilic bacterium found in estuarine and marine coastal ecosystems worldwide. Although the ability of V. parahaemolyticus to grow and proliferate in fluctuating saline environments is well known, the underlying molecular mechanisms of osmoadaptation are unknown. We performed an in silico analysis of V. parahaemolyticus strain RIMD2210633 for genes homologous to osmotic stress response genes in other bacteria. We uncovered two putative compatible solute synthesis systems (encoded by ectABC and betABI) and six putative compatible solute transporters (encoded by four bcct loci and two proVWX loci). An ectoine synthesis system clustered with a betaine/carnitine/choline transporter and a ProU transporter (encoded by homologues of proVWX from Escherichia coli), and a betaine synthesis system clustered with a ProU transporter (encoded by homologues of proVXW from Pseudomonas syringae). This is at least double the number present in V. cholerae, V. fischeri, or V. vulnificus. Six additional Vibrio species contain both ectABC and betABI, i.e., V. alginolyticus 12G01, V. angustum, V. harveyi BAA-1116, V. splendidus LGP32, Vibrio sp. strain MED222, and Vibrio sp. strain Ex25. V. harveyi HY01 and V. splendidus 12B01 only encoded the betaine system. In addition, V. alginolyticus had a compendium of systems identical to that found in V. parahaemolyticus. Comparative physiological analysis of RIMD2210633 with V. vulnificus YJ016, V. cholerae N16961, and V. fischeri ES114 grown at different salinities and temperatures demonstrated that V. parahaemolyticus had a growth advantage under all of the conditions examined. We demonstrate, by one-dimensional nuclear magnetic resonance analysis, that V. parahaemolyticus is capable of de novo synthesis of ectoine at high salinity whereas a ⌬ectB knockout strain is not. We constructed a single-knockout mutation in proU1, but no growth defect was noted, indicating transporter system redundancy. We complemented E. coli MKH13, a compatible solute transporter-negative strain, with bcct2 and demonstrated uptake of betaine at high salt concentrations.Vibrio parahaemolyticus is a moderate halophile prevalent in all of the coastal waters around the world, particularly in the warmer summer months (17). V. parahaemolyticus is found associated with zooplankton and phytoplankton and is present in sea sediment (18)(19)(20). V. parahaemolyticus is a pathogen of fish and humans and is the leading cause of seafood-associated bacterial gastroenteritis worldwide. Fish and shellfish, particularly oysters, are implicated as the major vectors for infection (5,7,27). Numerous outbreaks of V. parahaemolyticus infection in the Pacific Northwest have resulted in severe economic losses and closures in the seafood industry (27). A number of environmental factors affect the occurrence and distribution of V. parahaemolyticus, such as temperature, salinity, oxygen availability, plankton, and tidal flushing (8)(9)(10)(18)(19)(20) Because all of the V. parahaemolyticus strains in...
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