Characteristics of viable but nonculturable Vibrio parahaemolyticus induced under extended periods of cold-starvation with various NaCl concentrations

Abstract

This study was undertaken to examine the induction of VBNC states of Vibrio parahaemolyticus under prolonged cold-starvation with various NaCl concentrations and their responsive characteristics to maintain cell viability. V. parahaemolyticus entered the viable but nonculturable (VBNC) state in artificial sea water at 4{degrees}C within 80 day and persisted in the VBNC state for 150 days. During cold-starvation, bacterial cells were used to estimate their cell functions, including cytotoxicity, fatty acid composition, membrane potential, and morphology. Cytotoxic effect of V. parahaemolyticus cells against animal cell lines was decreased to below 50% after 80 days. VBNC V. parahaemolyticus cells showed decreasing levels of palmitic, vaccenic, and hexadecenoic acid on membrane, concomitantly with the formation of empty gaps between the cytoplasmic and outer membrane, in comparison with those of the pure cultures. Starvation at 4{degrees}C for 30 days resulted in a high increase in N-phenyl-1-napthylamine intensity within V. parahaemolyticus cells. Membrane potential and cellular composition were strongly affected by increasing NaCl contents of the microcosms after its evolution into the VBNC state. VBNC V. parahaemolyticus cells may undergo selected physiological changes such as the modulation of membrane potential and re-arrangement of cellular composition.