Optimum 37ºC, range 8-43 ºC. In live oysters growth does not occur below 13ºC. Grows in oysters at 30ºC. The organism can grow in shell stock after harvest and oysters need to be chilled as rapidly as possible to prevent this.
Optimum 7.8, range 5-10.
Grows in the presence or absence of oxygen
Optimum 0.98, range 0.96-0.997 (optimum 2.5% NaCl, range 0.5-6.0% NaCl)
May survive well under refrigeration by entering the viable but non-culturable (VNC) state in water. Survives quite well in oysters at 0-4ºC.
Survives at pH 5 in artificial media of low salinity at 5 and 20ºC for 72h.
Viable but non-culturable (VNC) cells
Can enter the VNC state and resuscitation is achieved simply by raising the temperature of the VNC forms in suspension.
D reduction times are approximately 50 min at 45ºC and 10 sec at 51ºC. A low temperature pasteurisation of 10 min at 50ºC has been suggested for shell stock oysters. Freezing reduces the population in oyster tissue by 95-99%, but the surviving population remain fairly stable during frozen storage.
D values at 21ºC are reported to be 30-50 min at pH 4.0, 1.5-4.5 min at pH 3.5 and 0.4-0.5 min at pH 2.0 (HCl acidulant). Inactivation is likely to be slower at lower temperatures. In oyster homogenates the D time at pH 6.2 and 40ºC is 12 min, and at 50ºC it is 2.7 min. When the pH is reduced to 4.6 the D time at 50ºC is 1.7 min.
Vibrio is inactivated more readily in seawater at salinity levels higher or lower than seawater.
A 1.0-1.5 kGy treatment for oysters has been proposed. This would inactivate the Vibrio but leave the oysters alive. A dose of 2 kGy produces an approximate 107 reduction of V. vulnificus in frozen shrimps. Raising the temperature can enhance the effect of radiation. For example raising the temperature from 25 to 40ºC had the effect of approximately halving the dose required to give the same kill.
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Gastroenteritis may result 16 hours after consuming contaminated food. For the more serious forms of the disease the mean time for onset of symptoms is 38 hours after consumption, with a range of 12 hours to several days, and septicaemia may follow within 36 hours of the initial symptoms. In wound infections the appearance of symptoms may be extremely rapid –a few hours.
Wound infections: causes swelling and tenderness of the affected limb. These account for about 45% of cases. Invasion of the blood stream (septicaemia) may follow wound infections. Primary septicaemia: follows the consumption of contaminated food. Death can occur rapidly in 50% of septicaemia cases, and in 25% of all wound infection cases. Initial symptoms include fever, malaise and chills. In 2/3 of cases skin lesions develop. Diarrhoea is rare in foodborne cases where these serious symptoms are manifest. These account for around 45% of cases. Gastroenteritis: may occur on its own but only in 5-10% of cases. This is characterised by vomiting, diarrhoea or abdominal pain. Hospitalisation occurs in around 91% of total cases.
At Risk Groups
People with impaired liver function or who are immunosuppressed are at risk groups for primary septicaemia. Of cases progressing to septicaemia 95% will have a pre-disposing condition. Wound infections may be acquired in people with normal immune systems. In the USA cases are mostly confined to the Gulf States where oysters are harvested from warm waters. It is the leading cause of foodborne illnesses that result in death in Florida.
Long Term Effects
Surgery to save life may require limb amputation.
The dose for healthy people is unknown, but in at risk groups it may be less than 100 cells.
Antibiotics (tetracycline alone or in combination with others) are used, treatment of symptoms is given and surgical removal of infected tissue or amputation may be necessary.
No record of human carriage.
Concentrated by filter-feeding marine life (e.g. mussels and oysters) growing in waters containing the organism. Has been isolated from shellfish in New Zealand.
Shellfish, primarily oysters, are considered to be the most significant food involved in foodborne infections as they filter feed and concentrate the organism. In the USA 95% of all seafood-related deaths are due to this organism. Oysters have been reported to contain >105 / g in the summer months. Fish feeding on plankton and other fish may also carry high counts: a potential problem where fish are frequently eaten raw.
V. vulnificus is a normal inhabitant of the marine environment, but is only detected in large numbers when the seawater temperature rises above approximately 17°C. At temperatures lower than this it enters the VNC state.
Infection can occur by three routes: ingestion of contaminated food; contact of an existing wound with seawater; a wound occurring in the marine environment.