Loss of Sensitivity to Xylitol by Streptococcus mutans LG-1

The effect of xylitol on the growth of Streptococcus mutans LG-1 was investigated under various conditions. Concentrations of xylitol ranging from 0.5 to 2% increased the time usually needed by the cells to reach the stationary phase in the presence of 0.2% glucose, mannose, lactose, mannitol, or sorbitol. Xylitol had no effect in the presence of fructose or sucrose. The xylitol-mediated inhibition was not modified by temperature or pH variations or by the presence or absence of oxygen. Repeated culturing in the presence of xylitol plus one of the above-mentioned sugars enabled the bacterium to tolerate the presence of xylitol. The cells, however, were still unable to grow at the expense of xylitol. The results indicate that this adaptive process arose from a mutational event.