Objectives: Earlier studies have demonstrated that xylitol concentrations ranging between 0.5 and 1% inhibit S. mutans growth. Such concentrations can be measured in saliva for example after chewing xylitol gum with high xylitol content. Our aim was to find the lowest level of xylitol concentration still inhibiting S. mutans growth in vitro.
Methods: Two type strains of S. mutans, (NCTC 10449 and Ingbritt), and three clinical isolates of S. mutans (2366S, 267S, 124S) from three volunteers not using xylitol, were used in the experiments. The bacteria were grown at 37 ˚C in brain heart infusion medium (Difco, MI, USA) supplemented with xylitol. The xylitol concentrations ranged from 0.001% to 1%. The growth was followed for 24-26 h by measuring the absorbance of the medium at 660 nm. Quadruplicate samples were collected at each time point during the growth. T-test for independent samples was used to analyse differences between the growth curves. The level of significance was set at p<0.05.
Results: All five S. mutans strains were inhibited by 1% xylitol: NCTC 10449 60%, Ingbritt 58%, 2366S 67%, 267S 74% and 124S 21%. The lowest xylitol concentration showing statistically significant growth inhibition was 0.005% for NCTC 10449, Ingbritt, 2366S, and 267S, while for 124S it was 0.1%.
Conclusion: The results show that the growth of both type strains and clinical isolates of S. mutans were inhibited by low concentrations of xylitol. Thus much lower concentrations of xylitol than demonstrated earlier may be effective in inhibiting S. mutans in vivo.