Formation and characteristics of viable nonculturable Vibrio parahaemolyticus induced by sodium hypochlorite

This study investigated whether sodium hypochlorite (NaClO) can induce Vibrio parahaemolyticus (Vp) into viable but nonculturable (VBNC) state and change its characteristics. When exposed to 40 mg/L chlorine for 20 min, plate counts decreased from 10 6 CFU/mL to undetectable but fluorescent staining indicated that 11.94 ± 1.24% of cells still remained viable, suggesting that Vp had entered a VBNC state. Light microscopy showed that VBNC-Vp cells had changed from a short rod-shape to coccoid with a rough surface , aggregation, and additional material in the intercellular spaces . In VBNC-Vp cells, intracellular pH i and respiratory activity were lower than in normal cells and the ATP concentration was 81.25 ± 1.64% in normal cells. VBNC-Vp cells exhibited lower surface zeta potential and reduced adhesion and invasion capacity compared to normal cells but their ability to survive in food-associated stresses was markedly enhanced. RT-qPCR results revealed that changes in morphology, metabolism, and adhesion of VBNC-Vp cells may be due to down-regulation of mreB , cysD , atpA , ompA , flaA , and flgM genes. The potential adversity-resistant capacity of VBNC-Vp cells were due to soxR and katG up-regulation. Overall, NaClO induced Vp into a VBNC state, thereby altering its biological properties to withstand adverse conditions.