Our bodies are under siege, constantly fighting back assaults from disease-causing bacteria. But we are also home to many harmless bacterial species that are share our bodies to no ill effects. Now, it seems that these ‘commensals’ could be our hidden allies against their harmful cousins. In one such ally, a group of scientists has just discovered a potential new weapon against Staphylococcus aureus.

But S.aureus doesn’t have our noses to itself. It has to jostle for space with a close relative called Staphylococcus epidermidis. It’s the most common commensal in our noses and, indeed, the most common contaminating bacterium in laboratory equipment. S.epidermidis is harmless, except in people whose immune systems have been compromised. But more interestingly, it has