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Vibrio spp. are isolated continuously from the estuarine, marine and sediment environments and seafood. The consumption of and/or contact to contaminated seawater or food can lead to infections in humans. V. parahaemolyticus can cause human gastroenteritis via consumption of contaminated raw or not thoroughly heated seafood.
In its natural habitat V. parahaemolyticus cell is forced to remain in the stationary phase or the viable but non-culturable (VBNC) state for survival.
The stationary phase is the common phase for bacterial survival in the environment. The metabolism of bacterial cells in the stationary phase is active but altered. Moreover, the resistance of stationary phase cells is greater to variety of stresses.
The viable but non-culturable (VBNC) state is referred to as enabling survival of especially non-sporulating bacteria, including Vibrio spp., in unfavourable or even hostile environments. The VBNC state can be induced by numerous factors, such as low temperature, depleted nutrient and adverse pH. Although bacterial VBNC cells are non-culturable on any routine laboratory medium, they maintain the ability of infection as the virulence genes are still expressed.
In this thesis, whole transcriptomic profiling of V. parahaemolyticus in the three phases (exponential and early stationary phase, the VBNC state) was performed. Studies on the global gene expression of V. parahaemolyticus demonstrated a broad adaptation of expression induced via the early stationary phase and the VBNC state. Among the 4820 investigated genes, 172 genes were induced while 61 genes were repressed totally. The altered processes were shown to be important for bacterial survival in the stationary phase against many stresses.
In the VBNC state compared with exponential and early stationary phase, up-regulated gene expression was also dominant. Totally 509 induced genes and 309 repressed genes among 4820 investigated genes were altered by more than fourfold. All these processes were shown to be of importance for the VBNC state maintenance. Massive regulations have been found, indicating that VBNC cells are active.
Until now it remains unclear what the incidence of food associated outbreaks caused by the food pathogenic VBNC state bacteria is. As the common detection methods depend on the CFU count and therefore growing cells, VBNC state bacteria avoid detection. Our research adds new data which might support the development of new methods for detection of not only V. parahaemolyticus VBNC cells but also other food pathogenic VBNC state bacterial cells.