Microbiology · Gram-negative cocci
Neisseria meningitidis !
- Bacterium
- Gram-negative
- Droplet
- Exam priority: high
A throat bacterium that can cause meningitis and a bloodstream infection with skin spots that worsens within hours.
Updated 2026-11-01
Also called: meningococcus
At a glance
- Gram
- Gram-negative
- Shape
- Coffee-bean diplococcus
- Oxygen
- Aerobic
- Family
- Neisseriaceae
- Stain
- Gram: red diplococci, often inside neutrophils in CSF
Morphology
- Gram-negative diplococci with flat facing sides
- Polysaccharide capsule defines the serogroups (A, B, C, W, X, Y)
- Oxidase-positive; ferments glucose and maltose
- Grows on chocolate agar and Thayer-Martin
Transmission
- Respiratory droplets and throat secretions during close or long contact (household, kissing, dormitories, barracks)
- Many healthy people carry it in the nasopharynx without illness
- Droplet precautions until 24 hours after an effective antibiotic is started
Reservoir: Humans only (nasopharynx)
Isolation precautions
What the care team adds to standard precautions.
- Droplet
- Surgical mask within about a metre; single room.
Virulence factors
- Capsule: blocks phagocytosis and complement lysis
- Lipooligosaccharide (LOS): endotoxin that drives shock, disseminated intravascular coagulation and vessel damage
- Pili and membrane proteins: attachment to nasopharyngeal epithelium
- IgA protease: cleaves mucosal IgA
- Sheds endotoxin-rich membrane blebs, which explains how severe the sepsis can be
Diseases it causes
- Acute bacterial meningitis, mainly in infants, adolescents and young adults Bacterial meningitis →
- Meningococcemia: sepsis with petechiae and purpura that do not blanch Meningococcal disease (meningococcemia) →
- Septic shock with disseminated intravascular coagulation and adrenal hemorrhage (Waterhouse-Friderichsen syndrome) Sepsis and septic shock →
Clinical picture
- Fever, headache, neck stiffness, photophobia and confusion
- A non-blanching petechial or purpuric rash is a red flag
- Infants: irritability, poor feeding, bulging fontanelle
- Can go from mild symptoms to shock within hours
Diagnosis
- Lumbar puncture: cloudy CSF with neutrophils, low glucose and high protein; it must not delay antibiotics
- CSF Gram stain: Gram-negative diplococci
- Blood and CSF culture on chocolate agar (reference test)
- PCR on blood or CSF, useful after antibiotics have been given
Treatment
A medical emergency: immediate intravenous antibiotic with a third-generation cephalosporin (ceftriaxone or cefotaxime); penicillin when the strain is susceptible. Strains with reduced penicillin susceptibility have been reported.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Conjugate vaccines against serogroups A, C, W and Y, and protein-based vaccines against serogroup B
- Chemoprophylaxis for close contacts (rifampicin, ciprofloxacin or ceftriaxone), ideally within 24 hours
- Droplet precautions for health workers
- Testing for complement deficiency after repeated infections
Vaccine: Conjugate vaccines (ACWY, and the pentavalent ACWYX) and serogroup B vaccines exist. In Colombia it is not part of the routine PAI schedule for all children; it is used for risk groups and travelers.
Test yourself
Think of the answer, then tap the question to see it.
A teenager has fever, neck stiffness and non-blanching petechiae. Which isolation precaution applies?
Droplet precautions (on top of standard) until 24 hours after an effective antibiotic is started.
Which immune defect predisposes to repeated meningococcal infections?
Deficiency of the terminal complement components (C5 to C9), or C5 blockade with eculizumab.
What is Waterhouse-Friderichsen syndrome?
Shock with bilateral adrenal hemorrhage and acute adrenal failure during fulminant sepsis, classically meningococcal.
Which N. meningitidis component is the basis of its conjugate vaccines?
The capsular polysaccharide, linked to a carrier protein.
Which antibiotics are used as chemoprophylaxis for contacts?
Rifampicin, ciprofloxacin or ceftriaxone.
Related
Related conditions
← Back to the group: Gram-negative cocci
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Chapter 14: Meningococcal Disease (CDC, 2024); Meningitis (WHO, 2026); About Meningococcal Disease (CDC, 2026); Fichas y Protocolos (Instituto Nacional de Salud (INS), Colombia, 2026).
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Representative model, for educational purposes only.