Bacteria are all over us, inside and out. Jiri Hulcr recently found 1,458 species of bacteria "new to science" in a small sample of human belly buttons. What we know about our little passengers and how they affect our bodies is dwarfed by what we do not. That can be disconcerting to think about, especially when some of them are undermining us.

In particular, some bacteria in our own intestines seem to have turned against us. Research this week in the New England Journal of Medicine led by Dr. Stanley Hazen at the Cleveland Clinic tells how they digest a compound called choline and turn it into trimethylamine N-oxide (TMAO).

TMAO is the new big thing in heart disease: higher levels of TMAO predict more heart attacks, strokes, and death:

Based on data from 4,000 patients at the Cleveland Clinic ( New England Journal of Medicine

Where does TMAO come from, and how do we stop it?

One place is carnitine, which is in red meat. Another is choline, which is a product of lecithin in egg yolks. Carnitine and choline are broken down by bacteria in our guts, which, we now know, turn them into TMAO.

In this study people ate two eggs, which increased the level of TMAO in their blood. If they took an antibiotic before eating the eggs, though -- which killed some of this subversive intestinal bacteria -- their TMAO level did not go up.