Neisseria meningitidis
A Gram-negative diplococcus causing epidemic meningitis and sepsis.
Neisseria meningitidis, often referred to as the meningococcus, is a Gram-negative diplococcus bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life-threatening sepsis. It is an exclusively human pathogen, spread through saliva and respiratory secretions, and is the only form of bacterial meningitis known to occur epidemically, mainly in Africa and Asia.
- type
- Gram-negative diplococcus
- size
- 0.6–1.0 micrometers
- carrier_rate
- 8–25% of adults (nasopharynx)
- mortality_rate
- about 10% (meningitis); about 50% (septicaemia)
- known_for
- causing epidemic bacterial meningitis and meningococcemia
- serogroups
- A, B, C, W135, X, Y (six main disease-causing types)
Lore & Background
Neisseria 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, thought to result from its inability to get iron from sources other than human transferrin and lactoferrin. The bacterium is referred to as a coccus because it is round, and more specifically a diplococcus because of its tendency to form pairs. It infects host cells by sticking to them with long thin extensions called pili and the surface-exposed proteins Opa and Opc.
Reader's Guide
Neisseria meningitidis is significant as the causative agent of meningococcal meningitis and septicaemia, diseases that can rapidly progress to death. Meningococcal meningitis initially produces general symptoms like fatigue, fever, and headache and can rapidly progress to neck stiffness, coma and death in 10% of cases. Septicaemia carries an approximate 50% mortality rate over a few hours from initial onset. The bacterium's lipooligosaccharide acts as an endotoxin responsible for septic shock and hemorrhage. Its polysaccharide capsule prevents host phagocytosis, and it produces an IgA protease to evade the humoral immune system. The multiple subtypes (six main capsular types: A, B, C, W135, X, Y) have hindered development of a universal vaccine. Current guidance in the United Kingdom recommends immediate intravenous antibiotics if meningococcal meningitis or septicaemia is suspected, even though this may reduce laboratory confirmation. The bacterium's genome contains genes that undergo phase variation, a mechanism that helps it evade the host immune system.
Did You Know?
- About 10% of adults are carriers of the bacteria in their nasopharynx.
- It causes the only form of bacterial meningitis known to occur epidemically, mainly in Africa and Asia.
- Meningococcal septicaemia carries an approximate 50% mortality rate over a few hours from initial onset.
- The bacterium's genome contains more genes that undergo phase variation than any pathogen then known.
Frequently Asked Questions
Who is Neisseria meningitidis?
Neisseria meningitidis, commonly called the meningococcus, is a tiny Gram-negative diplococcus measuring roughly 0.6 to 1.0 micrometers. It is an exclusively human pathogen that colonises the nasopharynx of 8–25% of adults without ever causing illness.
What are Neisseria meningitidis's powers/role?
The meningococcus is best known for triggering epidemic bacterial meningitis and meningococcemia, a life-threatening form of sepsis. It transmits through saliva and respiratory secretions, so close personal contact is its primary route of spread.
How does Neisseria meningitidis's story end?
Once meningitis takes hold, the case-fatality rate sits around 10%, while meningococcemia pushes mortality to roughly 50%. Survivors of meningitis can still face lasting neurological damage, so the ending is far from guaranteed to be a happy one.
Why is Neisseria meningitidis important?
It holds the unique distinction of being the only bacterial meningitis documented to occur in true epidemics, particularly across the African meningitis belt and parts of Asia. That epidemic potential is what sets it apart from every other bacterial cause of meningitis.
What is Neisseria meningitidis's main 'cast' of variants?
Six principal serogroups—A, B, C, W135, X, and Y—account for the vast majority of invasive disease. These serogroups also define the targets of the vaccines developed to prevent the most dangerous strains.
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