Neisseria Meningitidis

Neisseria meningitidis, often referred to as meningococcus, is a bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life-threatening sepsis. N. meningitidis is a major cause of morbidity and mortality during childhood in industrialized countries and has been responsible for epidemics in Africa and in Asia. Upon Gram staining, it appears as a Gram-negative diplococcus and cultures of the bacteria test positive for the enzyme cytochrome c oxidase.

It exists as normal flora (nonpathogenic) in the nasopharynx of up to 5-15% of adults. It causes the only form of bacterial meningitis known to occur epidemically. Streptococcus pneumoniae (aka pneumococcus) is the most common bacterial etiology of meningitis in children beyond 2 months of age(1-3 per 100,000). Meningococci only infect humans and have never been isolated from animals because the bacterium cannot get iron other than from human sources (transferrin and lactoferrin).

Meningococcus is spread through the exchange of saliva and other respiratory secretions during activities like coughing, kissing, and chewing on toys. It infects the host cell by sticking to it using Trimeric Autotransporter Adhesins (TAA). Though it initially produces general symptoms like fatigue, it can rapidly progress from fever, headache and neck stiffness to coma and death. The symptoms of meningitis are easily confused with those caused by other organisms such as Hemophilus influenzae and Streptococcus pneumoniae. Death occurs in approximately 10% of cases. Those with impaired immunity may be at particular risk of meningococcus (e.g. those with nephrotic syndrome or splenectomy; vaccines are given in cases of removed or non-functioning spleens).