BACTERIA · Gram-negative diplococci
Neisseria meningitidis
Neisseria meningitidis — Gram stain of CSF
Stain: Gram stain (CSF, 1000x)Morphology: Intracellular and extracellular gram-negative kidney-bean-shaped diplococci within neutrophilsYield: HIGHDifficulty: MEDIUM
Image: Wikimedia Commons · File:Neisseria_meningitidis_CSF_Gram_1000.jpg (CC BY-SA 4.0)
Key facts
**Pathogenesis**: Polysaccharide capsule (serogroups A, B, C, W, Y) blocks phagocytosis; LOS endotoxin drives massive cytokine release, DIC, and adrenal hemorrhage (Waterhouse-Friderichsen). **Diagnostic clue**: Gram-negative diplococci in CSF/petechiae; ferments BOTH maltose AND glucose (vs gonococcus = glucose only); grows on Thayer-Martin. **Virulence**: IgA protease, pili for nasopharyngeal attachment.
Boards buzzwords
- intracellular gram-negative diplococci
- kidney-bean shaped
- petechiae/purpura
- Waterhouse-Friderichsen
- maltose fermenter
Associated diseases
- Meningococcemia / septic shock
- Acute bacterial meningitis (adolescents, military, dorm)
- Waterhouse-Friderichsen syndrome
- Purpura fulminans
Treatment
Empiric ceftriaxone or penicillin G; rifampin/ciprofloxacin/ceftriaxone chemoprophylaxis for close contacts; MenACWY + MenB vaccines
Related organisms
Listeria monocytogenes
Gram-positive rod (facultative intracellular)
Mycobacterium tuberculosis
Acid-fast bacillus (mycolic acid cell wall)
Nocardia spp.
Gram-positive filamentous, partially acid-fast
Treponema pallidum
Spirochete
Mycobacterium leprae
Acid-fast bacillus (obligate intracellular)
Borrelia burgdorferi
Spirochete