Uncovering the Molecular Basis of Formation of Viable But Non-Culturable Cells

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Vibrio parahaemolyticus is a bacterium that is present in the marine environment and can be found in seawater, shellfish (such as oysters and mussels) and in crustacea (such as crab). This bacterium is the leading cause of seafood associated gastroenteritis worldwide. The bacterium can be destroyed during the cooking process, thus infection is generally associated with eating raw shellfish or cooked seafood products that have been cross-contaminated by raw shellfish or contaminated water. V. parahaemolyticus infections peak in the summer seasons, when sea temperatures are optimum for its growth. In the last 10 years the number of V. parahaemolyticus outbreaks has increased worldwide and has been as a result of rising sea temperatures. Climate change, globalisation and other drivers have also made Europe a hot spot for emerging infectious diseases including infections by V. parahaemolyticus. At present, detection of V. parahaemolyticus is not required under EU Food Hygiene legislation for testing of shellfish harvesting areas and ready to eat seafood products. Furthermore, disease associated with V. parahaemolyticus is not notifiable in the EU but in recent years there have been a number of outbreaks associated with contaminated seafood in Europe including Spain, Italy and Norway that have begun to change the significance of this pathogen in Europe. In the past it has been shown that when bacteria were incubated in sea water, the cells remained 'alive' but could not grow on culture media. However, they sometimes retain the ability to cause disease. These bacteria have been called 'viable but non-culturable' (VBNC) cells. The VBNC cells allow the bacteria to survive, until more favourable conditions arise. Cells in the VBNC state have low metabolic activity but, following environmental stimuli such as temperature upshift or nutrient supplementation, they can 'resuscitate' and restore their ability to grow on media. VBNC cells are not just important in a medical context because of their capacity to remain virulent and resuscitate in favourable conditions but they are also important in food safety. If VBNC cells are present in food samples and cannot be detected by conventional techniques, then the number of bacteria in food samples could be underestimated. In this project we will investigate the potential risk of V. parahaemolyticus VBNC present in seafoods and the risk they may pose to the seafood industry. We will also try to understand what genes present in V. parahaemolyticus cause this bacterium to enter the VBNC state and help in its resuscitation. Our aim is to help the seafood industry come up with ways to help manage the risk VBNC cells pose to the industry.