Their reasons for doing so seem to be that the depth of the colour is a good indicator of how free a male is of parasitic infection, and thus how good a father he will make.

ECONOMIST: Birds do it, bees do it | The

An absence of receptors should therefore be a good thing, because it closes off a shortcut to infection.

ECONOMIST: AIDS

So yes of course there's a problem with hospital-acquired infection but I think there are good plans on hand to deal with that.

BBC: News | BREAKFAST WITH FROST | Interview with Alan Milburn

The gut infection Clostridium difficile can be defeated by a cocktail of rival good bacteria, experiments in mice show.

BBC: 'Faecal transplant' clue to treating gut bug

The 42-year-old secretary and mother of three in Chandler, Arizona, had developed a nasty intestinal infection, the kind that sometimes occurs when antibiotics kill your body's good bacteria along with the bad and lower your defenses to other invaders.

CNN: Best cure for stomach troubles-- which probiotics work and why