Saturday, September 10, 2016

Guest Post- Vibrio parahaemolyticus


I'm introducing Dr Pendru Ragunath (Associate Professor , School of Medicine, Texila American University Guyana, South America) whom I had the privilege of talking to. He has published a lot on V parahemolyticus and so, I requested him if he could please share some of his knowledge. He has happily sent me his thoughts which I'm posting here.


Global warming might increase the number of Vibrio parahaemolyticus outbreaks

Vibrio parahaemolyticus is a gram negative, halophilic bacterium that occurs in estuarine environments worldwide. It was first identified as a foodborne pathogen in Japan in 1950. By the late 1960s and early 1970s, V. parahaemolyticus was recognised as a cause of diarrhoeal disease worldwide, although most common in Asia and the United States of America. Seventy percent of the seafood-borne gastroenteritis cases in Japan are due to V. parahaemolyticus and in India, this organism accounts for about 10% of gastroenteritis cases admitted to the Infectious Diseases Hospital in Kolkata. With the emergence of a pandemic clone of V. parahaemolyticus, this organism has assumed significance in recent years. Vibrios concentrate in the gut of filter-feeding molluscan shellfish, such as oysters, clams and mussels, where they multiply and cohere. Although thorough cooking destroys these organisms, oysters are often eaten raw are the most common food associated with V. parahaemolyticus infection. 

However, not all strains of V. parahaemolyticus are pathogenic. Although the mechanism by which this bacterium causes enteric disease is not fully understood, clinical isolates most often produce either the thermo stable direct hemolysin (TDH) or TDH related hemolysin (TRH) encoded by tdh and trh genes, respectively. TDH and TRH are considered major virulence factors in V. parahaemolyticus. The occurrence of tdh and/or trh genes among environmental V parahaemolyticus isolates typically 1–10%, but this depends on location, sample, source and detection method. Detection of tdh bearing V. parahaemolyticus is conventionally studied by their ability to produce β-haemolysis on a high-salt blood agar called Wagatsuma agar. The reaction is called Kanagawa phenomenon (KP), which requires fresh human or rabbit blood and tends to give false positive reactions and 16% of KP-negative strains as studied on Wagatsuma agar were found to carry the tdh gene. There is no commercially available detection method for TRH. Therefore, it would be important to detect the virulence genes of V. parahaemolyticus in clinical samples as well as in seafood by DNA-based molecular techniques such as polymerase chain reaction (PCR) and colony hybridization.

Both genes, trh and tdh share approximately 70% homology. Similar to TDH, TRH also activates cl− channels resulting in altered ion flux. Although TDH and TRH correlate with pathogenic strains, they do not fully account for V. parahaemolyticus pathogenicity. Several studies have reported that some of the clinical strains do not contain tdh and/or trh. Even in the absence of these hemolysins, V. parahaemolyticus remains pathogenic indicating other virulence factors exist.

The atmosphere affects oceans, and oceans influence the atmosphere. Because of global warming, the temperature of the air rises, oceans absorb some of this heat and also become warmer. Overall, the world's oceans are warmer now than at any point in the last 50 years. The change is most obvious in the top layer of the ocean, which has grown much warmer since the late 1800s. This top layer is now getting warmer at a rate of 0.2°F per decade. Oceans are expected to continue getting warmer, both in the top layer and in deeper waters. Even if people stop adding extra greenhouse gases to the atmosphere now, oceans will continue to get warmer for many years as they slowly absorb extra heat from the atmosphere. 

Temperature has been found to be a major factor in both the seasonal and geographical distribution of V. parahaemolyticus in shellfish-growing areas of the temperate regions. V. parahaemolyticus bacteria grow in seawater and can end up in shellfish like oysters and clams. When water temperatures rise in the summer, the accumulations of the naturally occurring bacteria increase to the point that eating undercooked shellfish can give people nausea, fever and diarrhoea. Based on their results, a group of researchers from Netherlands, derived an empirical formula to predict the Vibrios concentration as a function of temperature. According to that study, for an average temperature increase of 3.7°C, V. parahaemolyticus illness risks were calculated to be two to three times higher than in the current situation. If such extreme situations occur more often during future summers, then the number of V. parahaemolyticus outbreaks might increase.


Raghunath, P., Pradeep, B., Karunasagar, I., and Karunasagar, I., 2007. Rapid detection and enumeration of trh-carrying Vibrio parahaemolyticus with the alkaline phosphatase-labeled oligonucleotide probe. Environmental Microbiology 9, 266-270. 

Raghunath, P., Acharya, S., Bhanumathi, A., Karunasagar, I., and Karunasagar, I., 2008. Detection and molecular characterization of Vibrio parahaemolyticus isolated from seafood harvested along the southwest coast of India. Food Microbiology 25, 824-830.

Raghunath, P., Karunasagar, I., and Karunasagar, I., 2009. Improved isolation and detection of pathogenic Vibrio parahaemolyticus from seafood using a new enrichment broth. International Journal of Food Microbiology 129, 200-203.

Kumar, K., Raghunath, P., Devegowda, D., Deekshit, V. K., Venugopal, M. N., Karunasagar, I. and Karunasagar, I. 2011. Development of monoclonal antibody based sandwich ELISA for the rapid detection of pathogenic Vibrio parahaemolyticus in seafood International Journal of Food Microbiology 145, 244-249. 

Raghunath, P., 2015. Roles of thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH) in Vibrio parahaemolyticus. Front. Microbiol. 5, 805.

- Pendru Raghunath

If you have any queries, please contact Dr Pendru Raghunath at or

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