Neisseria meningitidis, often referred to as meningococcus, is a Gram-negative bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life-threatening sepsis. The bacterium is referred to as a coccus because it is round, and more specifically a diplococcus because of its tendency to form pairs. About 10% of adults are carriers of the bacteria in their nasopharynx. As an exclusively human pathogen, it is the main cause of bacterial meningitis in children and young adults, causing developmental impairment and death in about 10% of cases. It causes the only form of bacterial meningitis known to occur epidemically, mainly in Africa and Asia. It occurs worldwide in both epidemic and endemic form.N. meningitidis is spread through saliva and respiratory secretions during coughing, sneezing, kissing, chewing on toys and through sharing a source of fresh water. It has also been reported to be transmitted through oral sex and cause urethritis in men. It infects its host cells by sticking to them with long thin extensions called pili and the surface-exposed proteins Opa and Opc and has several virulence factors. Signs and symptoms
Meningococcus can cause meningitis and other forms of meningococcal disease. It initially produces general symptoms like fatigue, fever, and headache and can rapidly progress to neck stiffness, coma and death in 10% of cases. Petechiae occur in about 50% of cases. Chance of survival is highly correlated with blood cortisol levels, with lower levels prior to steroid administration corresponding with increased patient mortality.
Other severe complications include Waterhouse–Friderichsen syndrome, a massive, usually bilateral, hemorrhage into the adrenal glands caused by fulminant meningococcemia, adrenal insufficiency, and disseminated intravascular coagulation.Not all instances of a purpura-like rash are due to meningococcal septicaemia; other possible causes, such as idiopathic thrombocytopenic purpura (ITP; a platelet disorder) and Henoch–Schönlein purpura, also need prompt investigation. Microbiology
N. meningitidis is a Gram-negative diplococcus since it has an outer and inner membranes with a thin layer of peptidoglycan in between. It is 0.6–1.0 micrometers in size. It tests positive for the enzyme cytochrome c oxidase. Habitat
N. meningitidis is a part of the normal nonpathogenic flora in the nasopharynx of up to 8–25% of adults. It colonizes and infects only humans, and has never been isolated from other animals. This is thought to result from the bacteriums inability to get iron from sources other than human transferrin and lactoferrin. Subtypes
Disease-causing strains are classified according to the antigenic structure of their polysaccharide capsule. Serotype distribution varies markedly around the world. Among the 13 identified capsular types of N. meningitidis, six (A, B, C, W135, X, and Y) account for most disease cases worldwide. Type A has been the most prevalent in Africa and Asia, but is rare/practically absent in North America. In the United States, serogroup B is the predominant cause of disease and mortality, followed by serogroup C. The multiple subtypes have hindered development of a universal vaccine for meningococcal disease. Pathogenesis
Virulence
Lipooligosaccharide (LOS) is a component of the outer membrane of N. meningitidis.