system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: after eating, we have to brush our teeth to stop our teeth getting eaten from bacteria, right? So where does the bacteria come from, if we get rid of them every day?
gpt
Bacteria are always present in your mouth, and brushing your teeth doesn't do anything to reduce their population. 

What brushing does is scrape off the bacterial colonies that build up on your teeth as plaques, reducing the damage their acidic secretions can do to your enamel.