The genus Neisseria includes both pathogenic and commensal species. Neisseria meningitidis and Neisseria gonorrhoeae are exclusive human pathogens with no reservoir outside of the human host. Both species are Gram-negative diplococci. While N. meningitidis (the meningococcus) often colonizes the nasopharynx of up to 30% of healthy individuals without causing disease, in rare cases the bacteria enter the bloodstream and cerebrospinal fluid causing sepsis and inflammation of the brain (meningitis).1

Neisseria meningitidis has been recognized as a global pathogen, responsible for local outbreaks of infection as well as pandemic disease. Although the species, together with the non-pathogenic Neisseria species, are members of the complex microbiota of the human pharynx, it is the only bacterium that is capable of generating epidemic outbreaks of meningitis, a disease that can rapidly lead to death even with optimal antibiotic and supportive treatment. It is usually accompanied by disseminated intravascular coagulation and high level of circulating bacterial endotoxins. In the United States, there are about 1500 reported cases of meningococcal meningitis each year.3,4

Neisseria species Neisseria species Source:

Neisseria meningitidis is transmitted via respiratory droplets. In order to effectively colonize the niches within the human host, the organism must compete with significant resident bacteria for space and nutrients, as well as evade host immune defences. People who lack or have a deficiency an antibody-dependent, complement-mediated immune bactericidal activity are most susceptible to neisserial disease. People with factor D and properdin deficiencies are also at higher risk. Individuals with deficiencies in serum mannose-binding lectin are predisposed to invasive meningitis, especially children.2,5

The highest attack rate of meningitis in Europe and United States is in the first year of life, whereas the highest carriage rate is found among teenagers and adults. Carriage is more common in the second and third decades of life, and more common among smokers than non-smokers. Carriage rates are known to be much higher in closed communities with crowded conditions, such military recruits training camps, prisons, and schools.5

Meningococcal infection is a medical emergency, and the earlier an effective antibiotic treatment is initiated the better the prognosis. The mortality rate for meningococcal meningitis is about 10%. The drug of choice remains intravenously administered penicillin G in very high doses. Patients need to be hospitalized because the course of the disease is often unpredictable.4 Vaccination is the most effective prophylaxis for sepsis and meningitis caused by Neisseria meningitidis (meningococcus).


  1. Caroline Attardo Genco, Lee Wetzler. Neisseria: Molecular Mechanisms of Pathogenesis
  2. Matthias Frosch, Martin C. J. Maiden. Handbook of Meningococcal Disease: Infection Biology
  3. Moselio Schaechter. Desk Encyclopedia of Microbiology
  4. Stephen H. Gillespie, Peter M. Hawkey (editors). Principles and Practice of Clinical Bacteriology
  5. Pharyngeal carriage of Neisseria species in the African meningitis belt. Kanny Diallo,a J Infect. 2016 Jun; 72(6): 667–677.



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