Vibrio parahaemolyticus is a gram-negative, curved, halophilic bacterium primarily found in warm coastal waters and responsible for acute gastroenteritis, often linked to the consumption of raw or undercooked seafood. It produces a thermostable hemolysin, which is a key virulence factor, and can cause symptoms like watery diarrhea and abdominal pain, typically requiring large quantities for infection. Treatment usually focuses on hydration, while prevention strategies include cooking seafood thoroughly and minimizing cross-contamination.

1. Vibrio parahaemolyticus

2. VIBRIO PARAHAEMOLYTICUS
 Vibrio parahaemolyticus is a curved, rod shaped, Gram-negative halophilic bacterium.
 It is oxidase positive, facultatively anaerobic (capable of both fermentative and respiratory metabolism) and non-spore
forming.
 It is motile, with a single polar flagellum.
 It is non sucrose fermenting and produces green to blue green colonies on TCBS Agar (Thiosulfate-citrate-bile salts-
sucrose agar).

3. ISOLATION AND IDENTIFICATION
 The enrichment media used for vibrios exploit their greater tolerance for alkaline conditions. In alkaline peptone water (pH
8.6-9.0) the incubation period must be limited to 8h to prevent overgrowth of the vibrios by other organisms. Tellurite/ bile sat
broth (pH 9.0-9.2) is a more selective enrichment medium and can be incubated overnight.
 The most commonly used selective and differential agar used for vibrios is thiosulfate/citrate/bilesalt/sucrose agar (TCBS).
 Vibrio is non sucrose fermenting and produces blue-green colonies.
 Clinical strains of V. parahaemolyticus can be serotypes for epidemiological purposes using a scheme based on 11
thermostable O antigens and 65 thermolabile K (capsular) antigens.

4. HABITAT AND OPTIMUM
CONDITIONS FOR GROWTH
 Vibrio parahaemolyticus is a marine bacterium widely found throughout the world in warm coastal and estuarine
waters, sediments and plankton. It is primarily associated with coastal inshore waters rather than open sea.
 It cannot be isolated in water temperature below 15◦C and cannot survive pressures encountered in deep waters.
 The survival of the organism in winter months when the temperature drops below 15◦C is attributed to its persistence in
sediments from where it may be recovered even when water temperatures are below 10◦C.
 Optimum NaCl concentration for growth is 2-4% but it can grow at levels between 0.5% and 8% . It dies off in distilled water.
Minimum a w for growth varies between 0.937 and 0.986 depending on the solute used.
 Optimum pH values are slightly above neutrality (7.5-8.5) and this ability of vibrios to grow in alkaline conditions up to pH11 is
exploited in procedures for their isolation.
 Optimum growth temperature of enteropathogenic vibrios is around 37°C . Usual minimum temperature in natural environment
is 10°C. It is less robust in extremes of temperature than V. cholerae.
 D49 for V. parahaemolyticus in clam slurry is 0.7 min. In other studies, 5 mins at 60°C produced only 4-5 log reductions in
peptone/3% NaCl. Pre growth of organism in the presence of salt is known to increase heat resistance.

5. Niche specialization of the Vibrionaceae. Although all
Vibrionaceae are aquatic, they can be found in a wide
range of niches. The four Vibrio species shown can
colonize fish and marine invertebrates and can be
associated with plankton and algae. Vibrio cholerae,
Vibrio parahaemolyticus and Vibrio vulnificus infect
humans. 99% of environmental strains of V.
parahaemolyticus are non-pathogenic.

6. DISEASE AND PATHOGENESIS
 DISEASE: Ingestion of bacteria in raw and undercooked seafood is the predominant cause of acute
gastroenteritis caused by V. parahaemolyticus. Infection can occur through fecal-oral route too.
 FOODS INVOLVED: Raw fish and raw shellfish are the main cause of V. parahaemolyticus food poisoning.
Occasionally, cooked fish and salted vegetables have been involved when cross contamination with raw fish has
taken place.
 INCUBATION PERIOD: Reported incubation period for V. parahaemolyticus food poisoning varies from 2h to 4
days though it is usually 9-25h.
 SYMPTOMS: Profuse watery diarrhea free from blood and mucus, abdominal pain, vomiting and fever. It is
more enteroinvasive than V. cholerae and penetrates the intestinal epithelium to reach the lamina propria.
 DURATION: Symptoms persist for about 72 hours, but can persist for up to 10 days in immunocompromised
individuals.
 MORTALITY: Low. Majority of the deaths occur in elderly debilitated people.
 INFECTIVE DOSE: Large numbers are required; 105 - 107 viable cells ingested.

7. PATHOGENESIS
 Pathogenicity of V. parahaemolyticus is strains is strongly linked to their ability to produce a 22kDa, thermostable,
extracellular haemolysin (TDH). The major key virulence factor associated with V. parahaemolyticus is TDH (thermostable
direct hemolysin).
 When tested on a medium known as Wagatsuma’s agar, the haemolysin can lyse fresh human or rabbit blood cells but not
those of horse blood. A thermostable extracellular substance is responsible for the hemolytic reaction. This hemolysis is known
as the Kanagawa reaction.
 The haemolysin has also been shown to have enterotoxic, cytotoxic and cardiotoxic activity.
 Most (96.5%) strains from patients with V. parahaemolyticus food poisoning produce hemolysin and are designated
Kanagawa positive (Ka+) while 99% of environmental isolates are Ka- (producing heat labile hemolysin).
Ka- strains producing TRH ( TDH Related Hemolysin) but not TDH have also been found to cause gastroenteritis.
 Studies have found that ingestion of 107 - 1010 Ka- cells has no effect, whereas 105 - 107 Ka+ cells produce illness. A
number of other virulence factors have been described but not studied very intensively.

8. TREATMENT AND PREVENTION
TREATMENT :
Not necessary in most cases of V. parahaemolyticus infection.
There is no evidence that antibiotic treatment decreases the severity or the length of the illness.
Patients should drink plenty of liquids to replace fluids lost through diarrhea.
In severe illnesses, antibiotics such as tetracycline, ampicillin or ciprofloxacin can be used based on antibiotic susceptibility.
 PREVENTION:
 Thermal processing is a common approach to inactivating V. parahaemolyticus residues in seafood.
 Low-temperature freezing (at –18°C or –24°C) or high-temperature treatment (>55°C) for 10 min is reported to effectively
inactivate or kill V. parahaemolyticus in oysters
 High-pressure processing (HPP) is another method that has also been used to destroy pathogenic microorganisms in
seafood, and has been used extensively to inactivate V. parahaemolyticus in oysters
 Irradiation is another important method of eliminating V. parahaemolyticus from oysters.
 Chemical reagents have been developed to reduce the bacterial contamination in seafood, including chlorine, electrolyzed
oxidizing water and iodophors.
 Canning and vacuum sealing are also done for preservation.

9.  Ice or refrigerate fish immediately after harvesting and keep at low temperatures until consumed.
Avoid eating raw fish and raw shellfish.
Cook fish adequately.
Take care to prevent cross contamination from raw fish to cooked fish.

10. EPIDEMIOLOGY
 The identity of V. parahaemolyticus as a food borne gastroenteritis agent was made first by
Fujino in 1951. It is the leading cause of food poisoning in Japan, accounting for 24% of bacterial
food poisoning between 1965 and 1974.
 This has been linked with the national culinary habit of consuming raw or partially cooked fish,
although illness can also result from cross-contamination of cooked products in the kitchen.
 T he 1951 outbreak in Japan was traced to a boiled and semidried young sardines preparation,
with 272 victims and 20 deaths.
 The next two outbreaks occurred in Japan in 1956 and I960.
 Risk management measures implemented in 2001 included the establishment of a microbiological
limit for V. parahaemolyticus in food, a standard for food processing, and a standard for food
storage. Since then, the number of outbreaks and cases decreased drastically to 14 and 280,
respectively, in 2009.

11. The first outbreak in the United States occurred in 1971. Steamed crabs and crab salad were the vehicle foods, and 425 of
approximately 745 persons at risk became ill.
1998. V. parahaemolyticus was the etiological agent in this outbreak among 23 persons living in Connecticut, New Jersey,
and New York who ate raw oysters and clams harvested from Long Island Sound, NY.
 1997. Raw oysters were the source of Vibrio parahaemolyticus in this outbreak in British Columbia, Washington, Oregon,
and California, and there were 209 victims.