61C-29 |
Effects of acid adaptation on subsequent acid, heat and freeze/thaw tolerance of Vibrio vulnificus |
W. BANG, Dept. Food Science and Technology, Mississippi State University, Box 9805, Mississippi State, MS 39762 and M. A. Drake, Dept. Food Science, North Carolina State University, Raleigh, NC 27695. V. vulnificus is a halophilic bacterium associated with U. S. coastal waters, which can cause foodborne disease and wound infections. Foodborne disease is most commonly associated with consumption of contaminated raw oysters. Sublethal stresses such as reduced pH may enhance survival and subsequent resistance to processing or control regimes. The objective of this study was to determine the effects of acid adaptation on subsequent acid, heat and freeze/thaw tolerance of V. vulnificus. Three strains of V. vulnificus (isolated from primary septicemia associated with raw oyster consumption) were used. Cells were propagated in tryptic soy broth with 2 % sodium chloride (TSBN2) and enumerated in TSAN2 agar pour plates at 37C. Stationary phase cells (12 h) were used. Survival of each strain was evaluated in TSBN2 (pH 5.0, 4.0, 3.5) at 23C. Each strain was acid adapted by transfer to TSBN2 pH 5.0 for 3 h at 37C. Following acid adaptation, cell aliquots (1 ml) were transferred to TSBN2 (pH 3.5) at 23C and acid tolerance determined. Freeze/thaw tolerance (23C/-20C) and heat tolerance (47C) were also determined. Control cells (no acid adaptation) were also evaluated. Initial populations (106 CFU/ml) did not decrease at pH 5.0 at 37C. D-values at pH 3.5 of the three strains were 4.1 - 5.1 min without acid adaptation. D-values of acid adapted cells at pH 3.5 increased to 6.0 - 9.0 min (p<0.05). Heat tolerance (47C) and freeze/thaw (-20C) tolerance were variable between the three strains (p<0.05), but were enhanced following acid adaptation (p<0.05). Sublethal acid stress does enhance subsequent acid resistance of V. vulnificus. This information will be helpful in the development of methods to minimize V. vulnificus risk.
Session 61C, Food Microbiology: General I
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