Keeping DNA Out, Letting It In
All three meningitis bacteria (meningococci, Haemophilus influenzae, and pneumococci) are able to soak up DNA from their environments; thus, they all exhibit substantial genetic diversity. Those whose cell walls stain Gram negative (meningococci and H. influenzae) use DNA uptake signal sequences to take up the DNA, while pneumococci, which stain Gram positive and thus possess a different kind of cell wall, use a unique and less well understood mechanism. Although these interesting and important scientific discoveries have little to do with the clinical management of meningitis, they reveal a lot about the basic biology of H. influenzae and other meningitis-causing bacteria. By using the molecular tools that permit bacteria to acquire new DNA from their environments, H. influenzae bacteria are able to refashion themselves. In this way, at least a few of the bacteria in the enormous population of bacteria that live in humans are able to cope with whatever challenging environment they happen to fall into, including their transit from the throat, where they normally live, to the blood and meninges, where they cause meningitis.