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

Neisseria meningitidis microscopic image — Gram-negative diplococci, Gram stain (CSF, 1000x)

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