Extracellular hydrolase activity of the cells of the oral bacterium Streptococcus mutans isolated from man and grown on glucose or xylitol

Cells of Streptococcus mutans were maintained for 18 months in medium containing either glucose or xylitol as the only added carbohydrate. Growth in 0.25 per cent xylitol was retarded by about 60 per cent as compared with the growth in glucose medium. The growth pattern in the presence of xylitol was similar to that obtained when no carbohydrates were added. No uptake of $\text{[}{}^{14}\text{C(U)]-}\text{xylitol}$ was observed with cells maintained for 18 months in xylitol. Extracellular enzyme activities, tested with 10 different $\text{N-}\text{l}\text{-}\text{aminoacyl}\text{-2-}\text{naphthylamines}$, $\text{N-}\text{carbo}\text{-2-}\text{naphthoxy}\text{-}\text{dl}\text{-}\text{phenylalanine}$, casein, azocoll, congocoll and a chromophore collagenase substrate, were significantly higher in the xylitol medium. Isoelectric focusing of proteins from the extracellular medium containing xylitol revealed enzymes hydrolysing $\text{N-}\text{l}\text{-}\text{methionyl}\text{-2-}\text{naphthylamine}$ and casein, not detected in the chromatograms of glucose-containing medium. Xylitol behaved as an inert carbohydrate with respect to the increases in the extracellular proteinase activities, and could be associated with a general increase in protein metabolism upon starvation of a fermentable carbohydrate (glucose). Similar increase in the proteinase activities occurs in whole saliva and dental plaque when xylitol is habitually consumed. Because of their non-specificity, these proteinases could attack salivary proteins and peptides in vivo.