Response of Vibrio parahaemolyticus to ethanol shock

In this study, the growth and survival of Vibrio parahaemolyticus in the presence of 0.0–8.0% ethanol was first examined. V. parahaemolyticus was then exposed to a sub-lethal dose of 5.0% ethanol for 30 and 60 min (ethanol shock). Morphological changes and alterations in cell leakage, thermal tolerance at 47 1C, and susceptibility to 8% ethanol and low temperature (4 and 18 1C) of V. parahaemolyticus caused by ethanol shock were investigated. In addition, recoveries of the ethanol-shocked cells of V. parahaemolyticus on thiosulfate–citrate–bile salts–sucrose agar (TCBS) and TSA–3.0% NaCl were also compared. The findings revealed that the presence of ethanol in TSB–3.0% NaCl at 6.0–8.0% and 5.0% or less, exerted bactericidal and partial growth inhibition effect, respectively, on V. parahaemolyticus. Recovery of ethanol-shocked cells of V. parahaemolyticus was significantly (Po0:05) less on TCBS than on TSA–3.0% NaCl. A significantly (Po0:05) marked increase of protein and nucleic acid material in the supernatant of cell suspension was found after cells of V. parahaemolyticus were exposed to ethanol shock. Extensive cell disruption, wrinkling and cell-wall pitting, indicative of cell-surface damage were also noted on the ethanol-shocked cells. Ethanol-shocked cells of V. parahaemolyticus exhibited a similar yet higher susceptibility at 4 and 18 1C compared with the control cells. Moreover, there was a marked increase in the thermal tolerance and resistance to 8.0% ethanol with cells of V. parahaemolyticus after ethanol shock. Finally, the duration of ethanol shock testing did not affect the extent of increased thermal tolerance. While cells of V. parahaemolyticus subjected to ethanol shock for 60 min showed an increase in their resistance to 8.0% ethanol, they also showed an increase in susceptibility at 18 1C, than those ethanol shocked for 30 min