Meningococcus is a gram-negative bacterium (diplococcal, in pairs) that can cause various diseases. Ca. 10% of the european population carry these bacteria in their nasopharynx without showing any symptoms of disease. Meningococci, like pneumococci, have a capsule and are transmitted by humans via droplet infection (coughing, sneezing, or kissing). They attach themselves to the nasopharyngeal mucosa, where they can stay for weeks or months. In case the immune system is weakened, e.g. due to another infection, these bacteria can reproduce, permeate the mucosae and cause meningitis or sepsis.