Pathways for lactose/galactose catabolism by Streptococcus salivarius.

Galactokinase and beta-galactosidase-deficient strains of Streptococcus salivarius were constructed to define the pathways for lactose and galactose catabolism. It was found that S. salivarius does not possess a lactose-specific phosphoenolpyruvate phosphotransferase system (PTS), that intracellular lactose was hydrolyzed by beta-galactosidase, and that galactose is catabolized exclusively through the Leloir pathway. The lack of a high-affinity PTS for lactose may reflect the higher availability of the substrates to soft tissue organisms, such as S. salivarius, compared to dental plaque bacteria.