Described are mutant Streptococcus thermophilus strains and mutant Lactobacillus delbrueckii subsp. bulgaricus strains that excrete glucose into milk when the milk is inoculated and fermented with such strains. Methods for obtaining such strains without genetic modification are described, including methods for obtaining such Streptococcus thermophilus strains by selecting and isolating from a pool of Streptococcus thermophilus strains derived from a galactose-fermenting Streptococcus thermophilus mother strain a pool of Streptococcus thermophilus strains which are resistant to 2-deoxyglucose, and selecting and isolating from the pool of Streptococcus thermophilus strains which are resistant to 2-deoxyglucose a Streptococcus thermophilus strain which exhibits a growth rate in M17 medium+2% galactose higher than its growth rate in M17 medium+2% glucose. The strains are useful for decreasing the lactose content of a fermented food product and for boosting growth of the probiotic BB-12®.