Abstract
Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1 (1073R-1) was selected from 139 Lactobacillus bulgaricus strains on the basis of exopolysaccharide (EPS) production and interferon-gamma-inducing activity. Oral administration of either EPS or yogurt fermented with this strain (1073R-1 yogurt) resulted in enhanced natural killer (NK) cell activity in animal studies. Therefore, we evaluated whether the intake of 1073R-1 yogurt can enhance human NK cell activity, and if it can inhibit the spread of respiratory tract infections, such as the common cold and influenza virus infections. The intake of 1073R-1 yogurt by healthy, elderly subjects was found to significantly reduce the risk of catching the common cold, and increased NK cell activity in subjects who had low levels of NK cell activity prior to intake. In addition, oral administration of either 1073R-1 yogurt or EPS prolonged the survival of influenza virus-infected mice. These results for 1073R-1 yogurt suggest the effect depends on the immunostimulatory EPS. Thus, we investigated ways to increase the amount of EPS in 1073R-1 yogurt. Several useful methods (increasing solids-not-fat, lowering the fermentation temperature, and addition of Na2HPO4, etc.) were explored, but prolonged fermentation time was a common problem for these methods. Further investigation is required to develop a yogurt which contains elevated levels of immunostimulatory EPS.
