Seasonal Variation in Abundance of Total and Pathogenic Vibrio parahaemolyticus Bacteria in Oysters along the Southwest Coast of India

Abstract

The seasonal abundance of Vibrio parahaemolyticus in oysters from two estuaries along the southwest coast of India was studied by colony hybridization using nonradioactive labeled oligonucleotide probes. The density of total V. parahaemolyticus bacteria was determined using a probe binding to the tlh (thermolabile hemolysin) gene, and the density of pathogenic V. parahaemolyticus bacteria was determined by using a probe binding to the tdh (thermostable direct hemolysin) gene. Furthermore, the prevalence of V. parahaemolyticus was studied by PCR amplification of the toxR, tdh, and trh genes. PCR was performed directly with oyster homogenates and also following enrichment in alkaline peptone water for 6 and 18 h. V. parahaemolyticus was detected in 93.87% of the samples, and the densities ranged from <10 to 10 4 organisms per g. Pathogenic V. parahaemolyticus could be detected in 5 of 49 samples (10.2%) by colony hybridization using the tdh probe and in 3 of 49 samples (6.1%) by PCR. Isolates from one of the samples belonged to the pandemic serotype O3:K6. Twenty-nine of the 49 samples analyzed (59.3%) were positive as determined by PCR for the presence of the trh gene in the enrichment broth media. trh-positive V. parahaemolyticus was frequently found in oysters from India.Vibrio parahaemolyticus is a halophilic bacterium that occurs in estuarine environments worldwide (5,13,14,16,18,19). This organism was first discovered in Japan in 1950 in association with a food poisoning case (9). V. parahaemolyticus infection can cause gastroenteritis in humans, and the illness is most frequently associated with the consumption of raw or undercooked seafood and seafood recontaminated with the bacterium after cooking (31). V. parahaemolyticus accounts for about 70% of the gastroenteritis associated with seafood in Japan (14), and in India about 10% of the cases of gastroenteritis in patients admitted to the Infectious Diseases Hospital in Kolkata are due to V. parahaemolyticus (3). However, not all strains of V. parahaemolyticus are pathogenic. It has been demonstrated that the Kanagawa phenomenon, a beta-hemolysis in high-salt blood agar (Wagatsuma agar), is associated with most clinical strains but with very few environmental strains (32, 38). The hemolysis is due to the production of a thermostable direct hemolysin (TDH) (30). A TDH-related hemolysin (TRH) produced by a Kanagawa phenomenon-negative strain was discovered during investigation of an outbreak of gastroenteritis in the Maldives Islands in 1985 (10, 11). TDH and TRH, encoded by the tdh and trh genes, respectively, are considered major virulence factors in V. parahaemolyticus (31). It has been reported that more than 90% of clinical isolates but less than 1% of environmental isolates produce TDH (7,22,33). In recent years, the incidence of V. parahaemolyticus infection has been increasing in many parts of the world, and this has been attributed to the emergence of a new clone of the O3:K6 serotype carrying only the tdh gene (24). Although various serovars of the...

An assessment of potential public health risk associated with the extended survival of indicator and pathogenic bacteria in freshwater lake sediments

“…High concentration and prolonged survival of pathogenic bacteria in sediments from the study area coupled with the filter feeding nature of the shellfishes pose direct or indirect health risk through the consumption of contaminated shellfish. Shellfish associated food borne illness has been reported from India and other Asian countries (Deepanjali et al, 2005). The results of the present study are of particular significance to public health because Vembanadu Lake is the life line of the people in that area as they use this water body for agriculture, fishing, transport and contact recreation.…”

Occurrence of potentially pathogenic Vibrio in oysters (Crassostrea gigas) and waters from bivalve mollusk cultivations in the South Bay of Santa Catarina

“…The tdh gene was detected in four strains, and trh was detected in 23 strains (Figure 2). Several studies have suggested a strong influence of temperature on the concentration of vibrio in marine waters [27][28][29][30] . However, this study only established a correlation with V. vulnifi cus (p < 0.05).…”

Total number, virulence genes, and heterogeneity of Vibrio parahaemolyticus in a single shellfish

“…It has been demonstrated that around 3-6% of V. parahaemolyticus isolated from the environment carry the virulence genes (tdh or trh) 7,8 . Thus it is not easy to isolate tdh + and/or trh + strains from seafood.…”

“…These haemolysins are encoded by the tdh and trh genes, respectively; either tdh, trh or both genes are present in most clinical isolates of V. parahaemolyticus 6 . However, only 3-6% of environmental isolates harbour these genes 7,8 . A classification based on combination of the serotypes of two antigens, somatic O and capsular-like K, have been established using clinical strains and serves as a useful tool in epidemiological investigations 9 .…”