How does streptococcus mutans (cavities) start and how does it spread?

Mother to child: It is believed that mother to child is how strep mutans is passed on. In some countries people don't get tooth decay. So, those people don't have strep mutans.

Infection: Streptococcus mutans, the bacteria that causes most of the carious lesions is usually passed from mother to baby by kissing. There is a study that shows if the mother chews a xylitol chewing gum, which reduces the levels of streptococcus mutans in the mother's mouth, the baby will develop fewer carious lesions.