29G-20 |
Resistance of Vibrio vulnificus to physical stresses following different acid adaptation times |
W. S. BANG, Dept. of Food Science & Technology, Mississippi State Univ., Campus Mailstop 9805, Mississippi State, MS 39762-9805 and M. A. Drake, Dept. of Food Science, North Carolina State Univ., Schaub Hall, Box 7624, Raleigh, NC 27695-7624. Vibrio vulnificus is natural inhabitant of estuarine and sea waters which can cause foodborne disease and wound infections. This bacterium is highly concentrated in filter feeding mollusks such as clams and oysters when these shellfish are harvested during summer months. Foodborne disease is most commonly associated with consumption of contaminated raw oysters. Exposure to sublethal pH in minimally processed foods may enhance resistance of this organism. The objective of this study was to determine the effects of different acid adaptation times on subsequent cold storage, heat, freeze/thaw, and acid tolerance of V. vulnificus. Three strains of V. vulnificus were used. Cells were propagated in tryptic soy broth with 2 % sodium chloride (TSBN2) and enumerated in TSAN2 agar pour plates at 37 C. Stationary phase cells (12 h) were used. Each strain was acid adapted by transfer to TSBN2 pH 5.0 for 0, 1, 3, 5, 10 and 15 h at 23 C. Following each timepoint of acid adaptation, cell aliquots (1 ml) were transferred to TSBN2 (pH 3.5) at 23 C and acid tolerance determined. Freeze-thaw tolerance (- 20C / 23C), heat tolerance (47C) and cold storage (5C and -80C) were determined. Control cells (no acid adaptation) were also evaluated. Initial cell populations (10E6 CFU/ml) were stable at pH 5.0 at 23 C through 15h. D-values at pH 3.5 of the three strains increased with increasing time of acid adaptation (p<0.05). Freeze/thaw and cold tolerance increased with acid adaptation time(p<0.05), but heat tolerance was not enhanced (p>0.05). Sublethal acid stress enhanced subsequent acid, freeze-thaw and cold tolerance of V. vulnificus. Resistance increased with increased exposure time to pH 5.0; peaking and stabilizing after 10 h. This information will be helpful in the development of processing techniques to minimize V. vulnificus risk.
Session 29G, Food Microbiology: General
|