Adaptive response to cold temperatures in Vibrio vulnificus

The effectiveness of rapid chilling or freezing of oysters to reduce Vibrio vulnificus levels in shellfish may be compromised by product handling proc edures that permit cold adaptation. When a V. vulnificus culture was shifte d from 35 degrees C to 6 degrees C conditions, it underwent transition to a non-culturable state. Cells adapted to 15 degrees C prior to change to 6 d egrees C condition, however, remain viable and culturable. In addition, cul tures adapted to 15 degrees C were able to survive better upon freezing at -78 degrees C compared with cultures frozen directly from 35 degrees C. Inh ibition of protein synthesis by addition of chloramphenicol in a V. vulnifi cus culture immediately prior to the exposure to the adaptive temperature e liminated inducible cold tolerance. These results suggest that cold-adaptiv e "protective" proteins may enhance survival and tolerance at cold temperat ures. In addition, removal of iron from the growth medium by adding 2,2'-Di pyridyl prior to cold adaptation decreased the viability by approximately 2 logarithm levels. This suggests that iron plays an important role in adapt ation at cold temperatures. Analysis of total cellular proteins on an SDS p olyacrylamide gel electrophoresis, labeled with S-35-methionine during expo sure at 15 degrees C, showed elevated expressions of a 6-kDa and a 40-kDa p rotein and decreased expression of an 80-kDa protein. These results suggest that, for V. vulnificus, survival and tolerance at cold temperatures could be due to the expression of cold-adaptive proteins other than previously d ocumented major cold shock proteins such as CS7.4 and CsdA. In this study, for the first time we have shown that exposure to an intermediate cold temp erature (15 degrees C) causes a cold adaptive response, helping this pathog en remain in culturable state when exposed to a much colder temperature (6 degrees C). This adaptive nature to cold temperatures could be important fo r shellfish industry efforts to reduce the risk of V. vulnificus infection from consuming raw oysters.