Helen FieldsScience Writer

I don’t know how you have fun at your house, but I celebrated Christmas Eve with a story about tooth decay for ScienceNOW. (Ok, I wrote it on the 23rd; it just went through final editing on the 24th.)

The thinking on tooth decay has changed a lot in the last few decades. The people who study oral health used to focus on one organism, Streptococcus mutans, as the culprit in cavities, churning out the acid that destroys enamel.

But now they realize that tons of microbes, from hundreds of species, live in your mouth. Your mouth is like a tropical rainforest, but with Streptococcus and Bifidobacterium and Lactobacillus instead of fig trees and monkeys and toucans. People who study dental disease – and intestinal disease, too – have realized they need to think about the mouth and gut like an ecological system.

The advances in molecular biology in the last couple decades have totally revolutionized the study of microorganisms. In the old days, if you wanted to know what was growing in someone’s mouth, you had to take a sample of goo, then grow it up in the lab to see what you had. The problem is, a lot of bacteria are hard to culture. They’re finicky eaters. Some won’t grow in the presence of oxygen. But now, scientists can take that goo, extract DNA, and census the bugs without having to culture them.

That means scientists are getting more of a handle on all the different jungles in your body. You are so majorly outnumbered by bacteria. There’s one of you and a bazillion of them. They live in your intestines, in your nose, in your mouth, on your skin. You’re even outnumbered at the cell level. There are more bacterial cells in and on your body than human cells. Don’t worry, you’re still mostly human if you measure by volume; bacterial cells are much, much smaller than mammal cells.

Photo: Bifidobacterium dentium, courtesy of the Ventura Lab