Effect of xylitol on growth of Streptococcus pneumoniae in the presence offructose and sorbitol

Xylitol is effective in preventing acute otitis media by inhibiting the gro wth of Streptococcus pneumoniae. To clarify this inhibition we used fructos e, which is known to block similar growth inhibition observed in Streptococ cus mutans. In addition, we evaluated the efficacy of sorbitol in inhibitin g the growth of pneumococci, as sorbitol is widely used for indications sim ilar to those for which xylitol is used. The addition of 5% xylitol to the growth medium resulted in marked growth inhibition, an effect which was tot ally eliminated in the presence of 1, 2.5, or 5% fructose but not in the pr esence of 1 or 5% glucose, 1% galactose, or 1% sucrose. This finding implie s that xylitol-induced inhibition of pneumococcal growth is mediated via th e fructose phosphotransferase system in a way similar to that in which muta ns group streptococcal growth is inhibited. The addition of sorbitol at con centrations of 1, 2,5, or 5% to the growth medium did not affect the growth of pneumococci and neither inhibited nor enhanced the xylitol-induced grow th impairment. Thus, it seems that xylitol is the only commercially used su gar substitute proven to have an antimicrobial effect on pneumococci.