There's a good chance you have: Field surveys show that the nasal cavities of one-third of U.S. residents are populated with the bug, which usually sits there not doing much but can cause low-grade inflammation, heart problems, pneumonia and septicemia.

Worse, some of us have drug-resistant versions of the microbe in our noses -- the famous MRSA (methicillin-resistant S. aureus) or another beast called VRSA (vancomycin-resistant S. aureus).

But some people seem resistant to the colonization. A report just published in the journal Nature goes a long way to explaining how that happens.

It was already known that some people are colonized with a bacterium that stops S. aureus from growing there -- one called Staphylococcus epidermidis. Now, thanks to 88 volunteers who allowed cotton swabs be stuck up their noses for the advancement of science, the scientists know several new things:

1) It's not just any old S. epidermidis that has this inhibitory effect. It's a subclass. We don't all have it.

2) That subclass sics it to S. aureus by secreting an enzyme that chews up the tough matrix that sticks all the bad staph bugs together. Once they're unstuck from this film, the body's immune system can attack them and kill them.

3) You can even add the enzyme itself to someone's nose and that'll clear up the bad-staph colonization.

4) MRSA and VRSA are affected in the same way as regular S. aureus.

Microbes have all kinds of tricks they use to discourage the growth of competitors -- antibiotics themselves were isolated from a mold after a scientist noticed bacteria wouldn't grow close to it.

But this, wrote the Japanese authors, is the first example of the film-chewing enzyme trick they had seen -- "a novel mechanism distinct from all known bacterial interference mechanisms." And yes, they note that this may have some medical applications.

--Rosie Mestel

Photo: Staphylococcus aureus (which is a lot less nice than this image suggests). Credit: Visuals Unlimited