Neisseria meningitidis

Quick Profile

• Classification: Gram-negative diplococcus
• Key labs: Culture on Thayer-Martin (chocolate agar with antibiotics), oxidase positive, ferments glucose and maltose
• Colonization: Nasopharynx of asymptomatic carriers
• Clinical style: Rapid fulminant disease with meningitis and septicemia

Identification And Classification

• Organism family: Neisseriaceae
• Distinguishes from N. gonorrhoeae: ferments maltose (gonorrhoeae does not)
• Polysaccharide capsule is the major virulence factor; serogroups B, C, W, and Y are vaccine-preventable

Reservoir And Transmission

• Exclusive human pathogen; nasopharyngeal carrier rate around 10% in healthy adults
• Respiratory droplet transmission
• Risk factors: Asplenia, complement deficiencies (C5–C9), crowded living (college dormitories, military barracks), sub-Saharan Africa travel (meningitis belt)

Virulence Factors And Pathogenesis

• Polysaccharide capsule prevents phagocytosis and complement lysis
• IgA protease cleaves secretory IgA on mucosal surfaces
• Pili mediate nasopharyngeal attachment
• Lipooligosaccharide (LOS) triggers severe inflammatory cascade
• Endotoxin release drives disseminated intravascular coagulation (DIC)

High-Yield Disease Patterns

Bacterial Meningitis

• Triad: fever, nuchal rigidity, altered mental status
• Kernig sign (resistance to knee extension when hip is flexed) and Brudzinski sign (neck flexion causes reflexive knee flexion)
• Most common cause of bacterial meningitis in adolescents and young adults

Meningococcemia

• Septicemia without meningitis
• Characteristic non-blanching petechial to purpuric rash on trunk and extremities
• Rapid progression to shock

Waterhouse-Friderichsen Syndrome

• Bilateral adrenal hemorrhage from fulminant meningococcemia
• Hallmark: sudden cardiovascular collapse with purpuric skin lesions and adrenal insufficiency

Diagnosis

• Lumbar puncture: elevated WBC (neutrophil predominant), elevated protein, decreased glucose
• Gram stain of CSF showing gram-negative diplococci
• Blood and CSF cultures before antibiotics when possible, but do not delay treatment
• PCR of CSF for rapid confirmation

Treatment And Resistance

Empiric Therapy

• IV ceftriaxone (third-generation cephalosporin) immediately; do not delay for imaging unless papilledema or focal neuro signs present
• Add dexamethasone to reduce inflammation-mediated neurologic damage

Prophylaxis For Close Contacts

• Rifampin, ciprofloxacin, or single-dose ceftriaxone IM

Vaccination

• Quadrivalent meningococcal conjugate vaccine (MenACWY) for serogroups A, C, W, Y
• Serogroup B vaccine (MenB) given separately; recommended for complement-deficient and asplenic patients

For antibiotic mechanisms, see Pharmacology: Antimicrobials.

Exam Traps

• The petechial rash is non-blanching; blanching rashes do not suggest meningococcemia
• Complement deficiencies (especially terminal C5–C9) markedly increase susceptibility to Neisseria species
• Never wait for CT scan before lumbar puncture unless there are specific indications (papilledema, focal neuro signs, immunosuppression, seizure); delaying antibiotics for imaging is dangerous