Researchers wanted to better understand xylitol’s effect on good oral bacteria, whether it affects these bacteria like it does S. mutans. They found, “Based on the findings of this study, xylitol consumption reduced S. mutans and S. sobrinus counts in saliva but appeared not to effect numbers of [the good bacteria] S. sanguinis and S. mitis in saliva. So, habitual consumption of xylitol reduces cariogenic streptococci levels without any effect on beneficial streptococci for the oral cavity.”
Bahador, A., Lesan, S., & Kashi, N. (2012). Effect of xylitol on cariogenic and beneficial oral streptococci: a randomized, double-blind crossover trial. Iranian Journal of Microbiology, 4(2), 75–81.