Illustration of Neisseria Meningitidis, a pathogen that is a leading cause of bacterial meningitis in adults. Here it is seen exiting blood vessels in the choroid plexus of the brain, where it intermingles with blood cells in the cerebrospinal fluid and circulates around the entire meningeal layer of the central nervous system. In the foreground, one pathogen attaches itself to an epithelial cell that line the choroid plexus.