Graduate Thesis Or Dissertation
 

Antimicrobial effects of wine on enteric pathogens in a model stomach

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  • There have been several epidemiological studies linking alcohol consumption to a decreased risk of contracting illness from foodborne bacterial contamination. To study this phenomenon, we examined the survival of Escherichia coli 0157:H7 and Salmonella typhimurium in grape juice and wine and then designed a model stomach to investigate the effect of wine consumption with a meal on the survival of these bacteria. In addition, we looked at the role and relative effects of wine acid and alcohol content on bacterial survival. To test the relative role of acid and alcohol content on bacterial survival, 500 mL aliquots of Chardonnay and Pinot Noir wines were vacuum distilled to produce a non-volatile fraction containing only acids and a volatile fraction containing only alcohol. These fractions were subsequently brought back to the original 500 mL volume with distilled water. For the survival studies, approximately 1 x 10⁷ CFU/mL of E. coli 0157:H7 or Salmonella was added directly to 25 mL of sterile-filtered Chardonnay and Pinot Noir juice, wine, non-volatile, and volatile fractions. These treatments were then plated on tryptic soy agar (TSA) at appropriate time intervals to determine maximum survival times. We observed that both E. coli 0157:H7 and S. typhimurium were inactivated in wine within 60 min. In grape juice, £. coli and S. typhimurium survived 3-12 d and 3 h-16 d, respectively. Survival in the volatile fractions was less than 48 h for both bacteria and in the non-volatile fractions E. coli and S. typhimurium both survived less than 24 h. To determine the antimicrobial effect of wine on the survival of food borne E. coli 0157:H7 and S. typhimurium we designed a model stomach system. In this system, varying amounts of jarred baby food, synthetic gastric fluid (SGF), and the test beverage were aseptically placed in a stomacher bag, inoculated with bacteria to a level of approximately 1 x 103 CFU/mL, and then mixed in a stomacher blender prior to each sampling. The stomacher bags were sampled at 0, 30,60,120, and 180 min by the pour plate method using TSA. The beverages tested in this system were Chardonnay and Pinot Noir wines and their respective fractions; water served as a control. Escherichia coli 0157:H7 showed little change in cell population when in the presence of 150 g SGF, 150 g food, and 50 g of test beverage, regardless of the beverage. Salmonella typhimurium, under the same conditions, showed a marked difference between test beverages. In the presence of 50 g of wine, S. typhimurium had a 66-100% reduction at 60 min and had attained 100% reduction after 120 min; without wine, a 33-94% reduction was attained at 60 min and a 60-99% reduction was attained at 120 min. In general we found that that the E. coli 0157:H7 was much more resistant to inactivation than was S. typhimurium in the model stomach. Also, we found that Chardonnay was more effective in inhibiting bacteria than Pinot Noir and that the non-volatile wine fractions were more inhibitory than the volatile fractions. These observations suggest that the antibacterial power of wine is highly acid dependent and that the consumption of wine with a meal may afford protection against certain types of food contamination.
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