Vibrio parahaemolyticus | |
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SEM image of V. parahaemolyticus | |
Scientific classification | |
Kingdom: | Bacteria |
Phylum: | Proteobacteria |
Class: | Gamma Proteobacteria |
Order: | Vibrionales |
Family: | Vibrionaceae |
Genus: | Vibrio |
Species: | V. parahaemolyticus |
Binomial name | |
Vibrio parahaemolyticus (Fujino et al. 1951) Sakazaki et al. 1963 |
Vibrio parahaemolyticus is a curved, rod-shaped, Gram-negative bacterium found in brackish[1] saltwater, which, when ingested, causes gastrointestinal illness in humans.[1] V. parahaemolyticus is oxidase positive, facultatively aerobic, and does not form spores. Like other members of the genus Vibrio, this species is motile, with a single, polar flagellum.[2]
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While infection can occur via the fecal-oral route, ingestion of bacteria in raw or undercooked seafood, usually oysters, is the predominant cause the acute gastroenteritis caused by V. parahaemolyticus.[3] Wound infections also occur, but are less common than seafood-borne disease. The disease mechanism of V. parahaemolyticus infections has not been fully elucidated.[4]
Clincal isolates usually possess a pathogenicity island (PAI) on the second chromosome. The PAI can be acquired via horizontal gene transfer and contains genes for several virulence factors. There are two fully sequenced variants of the Vibrio parahaemolyticus PAI with distinctly different lineages[5][6]. Each pathogenicity island variant contains a genetically-distinct Type III Secretion System (T3SS), which is capable of injecting virulence proteins into host cells to disrupt host cell functions or cause cell death via apoptosis. There are two known T3SS variants on Vibrio parahaemolyticus chromosome 2, known as T3SS2α and T3SS2β. These variants correspond to the two known PAI variants. Aside from the T3SS, two genes encoding well-characterized virulence proteins are typically found on the PAI, the thermostable direct hemolysin gene (tdh) and/or the tdh-related hemolysin gene (trh). Strains possessing one or both of these hemolysins exhibit beta-hemolysis on blood agar plates. There seems to be a distinct correlation between presence of tdh, trh, and the two known T3SS variants: observations have shown T3SS2α correlating with tdh+/trh- strains, while T3SS2β correlates with tdh-/trh+ strains [7] .
Outbreaks tend to be concentrated along coastal regions during the summer and early fall when higher water temperatures favor higher levels of bacteria. Seafood most often implicated includes squid, mackerel, tuna, sardines, crab, shrimp, and bivalves like oysters and clams. The incubation period of ~24 hours is followed by explosive, watery diarrhea accompanied by nausea, vomiting, abdominal cramps, and sometimes fever. Vibrio parahaemolyticus symptoms typically resolve with-in 72 hours, but can persist for up to 10 days in immunocompromised individuals. As the vast majority of cases of V. parahaemolyticus food infection are self-limiting, treatment is not typically necessary. In severe cases, fluid and electrolyte replacement is indicated.[2]
Additionally, swimming or working in affected areas can lead to infections of the eyes or ears[8] and open cuts and wounds. Following Hurricane Katrina, there were 22 vibrio wound infections 3 of which were caused by V. parahaemolyticus and 2 of these led to death.
Hosts of Vibrio parahaemolyticus include:
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