Adaptation and resistance of Vibrio vulnificus to environmental stresses

The effects of cold storage and starvation on the subsequent heat resistance and freeze thaw resistance of V. vulnificus were studied and the effects of time of acid adaptation on subsequent cold storage, heat, freeze-thaw, acid tolerance of V. vulnificus were determined. Three strains of V. vulnificus were evaluated. V. vulnificus (ATCC 27562) was isolated from human blood and V. vulnificus MO6-24 strain was isolated from a primary septicemia case associated with raw oyster consumption. V. vulnificus 304 C strain was isolated from oyster (Alabama). After cold or starvation stress, freeze-thaw tolerance (−20°C/23°C), heat tolerance (47°C) and cold storage (5°C) were determined. Cold stress had no effect on freeze thaw resistance. Starvation enhanced freeze-thaw resistance compared to controls for one strain. V. vulnificus was very heat sensitive. Control cells and stressed cells, (106 CFU/ml), were inactivated within 12 min at 47°C. Starvation stress increased heat tolerance for one strain, but differences were small. Cold stress had no effect on heat resistance. Cold adaptation (holding 4 h at 15°C) enhanced cold storage tolerance at 5°C. Each strain was acid adapted by transfer to TSBN₂ pH 5.0 for 0, l, 3, 5 and 10 h at 23°C. Following each time point of acid adaptation, acid tolerance determined within TSBN₂ (pH 3.5) at 23°C. Initial populations (106 CFU/ml) were stable at pH 5.0 at 23°C for 10h. D-values at pH 3.5 of the three strains increased with increasing time of acid adaptation. Freeze-thaw tolerance increased when time of acid adaptation increased, but heat tolerance was not enhanced. Environmental stress conditions such as starvation, cold and acid stresses can provide protection to cold, freeze-thaw, and acid conditions. These responses should be considered when harvesting and handling raw seafoods and when processing minimally processed seafoods.