Utilization and acid production of β-galactosyllactose by oral streptococci and human dental plaque

beta -Galactosyllactose is a trisaccharide containing the beta -galactosidic linkage at the nonreducing end. The purpose of this study was to determine whether certain oral streptococci could utilize four kinds of beta -galactosyllactoses. Three of four beta- galactosyllactoses were unable to support growth of the oral streptococci and to be a substrate for producing acid from the cell suspensions and dental plaque. 4'-beta -Galactosyllactose supported growth of Streptococcus sanguis ATCC 35105, ATCC 49298, Streptococcus mitis ATCC 15914, Streptococcus oralis ATCC 35037, ATCC 10557 and Streptococcus milleri 10707 and produced acid from dental plaque. Although beta -galactosidase activities were observed in all the strains, 4'-beta -galactosyllactose could not be used as a carbon source for the growth of mutans streptococci. Enzymes metabolizing 4'-beta -galactosyllactose were induced when S. oralis ATCC 10557 was cultured in medium containing galactose. These results suggested that 4'-beta -galactosyllactose could be as cariogenic as lactose if it is consumed frequently and retained for a long period in the mouth.