Caught in the crossfire

Humans suffer collateral damage as microbes battle it out. Guess we've become the microbe's turf eh?

When S. pneumoniae is forced to share space with Haemophilus influenzae, another common and ordinarily asymptomatic bacterium, the two begin a tussle for space. But H. influenzae has an extra trick up its sleeve, calling on our immune system to help get rid of its competitor by recruiting white blood cells called neutrophils, which surround and attack the S. pneumoniae bacteria.

This of course forces S. pneumoniae to respond ...

Many strains of S. pneumoniae exist, each coated with a thick sugar capsule. In some strains, the capsule is particularly protective, and appears to act as armour against the host's immune response. This allows the bacterium to enter the blood stream where it can go on to replicate and cause serious diseases such as pneumonia, bacteraemia (blood infection), septicaemia and meningitis.