Taxonomic Classification
- Kingdom: Bacteria
- Phylum: Proteobacteria
- Genus: Neisseria
- Species: Neisseria meningitidis
- Commonly known as meningococcus
It is a Gram-negative, aerobic diplococcus that typically appears as kidney-shaped paired cells under the microscope.
Microbiological Characteristics
- Gram-negative organism with an outer membrane containing lipooligosaccharide.
- Possesses a polysaccharide capsule, a major virulence factor.
- Oxidase positive and catalase positive.
- Colonises the human nasopharynx.
The capsule helps the bacterium evade host immune responses and is central to disease severity.
Serogroups
Neisseria meningitidis is classified into serogroups based on capsular polysaccharides. The most clinically significant are:
- Serogroup A
- Serogroup B
- Serogroup C
- Serogroup W
- Serogroup Y
Different serogroups predominate in different geographical regions.
Transmission
- Spread through respiratory droplets and close contact.
- Transmission occurs via coughing, sneezing, or prolonged contact.
- Asymptomatic carriage in the nasopharynx is common.
Crowded environments such as hostels, military barracks and schools increase risk.
Diseases Caused
Meningococcal Meningitis
- Inflammation of the meninges surrounding the brain and spinal cord.
- Symptoms include fever, neck stiffness, headache, photophobia and altered consciousness.
Meningococcemia
- Bloodstream infection.
- May cause septic shock, disseminated intravascular coagulation and multi-organ failure.
- Characteristic purpuric or petechial rash.
Rapid progression can make the infection life-threatening within hours.
Pathogenesis
- Initial colonisation of nasopharynx.
- Invasion of bloodstream.
- Crossing of blood-brain barrier in meningitis.
- Endotoxin release contributes to severe inflammatory response.
Diagnosis
- Gram stain and culture of cerebrospinal fluid or blood.
- Polymerase chain reaction for rapid detection.
- Antigen detection tests in some settings.
Treatment
- Immediate antibiotic therapy is critical.
- Commonly treated with third-generation cephalosporins.
- Early intervention significantly reduces mortality.
Prevention
Vaccination
- Polysaccharide and conjugate vaccines available for major serogroups.
- Vaccination recommended for high-risk groups.
Chemoprophylaxis
- Close contacts may receive preventive antibiotics.
Public Health Significance
- Can cause outbreaks and epidemics.
- High mortality if untreated.
- Major cause of bacterial meningitis worldwide.
Neisseria meningitidis is a medically significant pathogen with epidemic potential, requiring rapid diagnosis, early treatment and strong vaccination strategies to prevent severe morbidity and mortality.
