guts

Though bacteria are everywhere -- from the air we breathe and the food we eat to our guts and skin -- the vast majority are innocuous or even beneficial, and only a handful pose any threat to us.

What distinguishes a welcome microbial guest from an unwanted intruder?

Scientists have discovered two key proteins that guide one of the two groups of pathogenic bacteria to make their hardy outer shells -- their defense against the world.

The work could allow researchers to create new antibiotics, they said.