Neisseria

General Characteristics

• Gram stain: Gram-negative diplococci, often intracellular (within neutrophils).
• Shape: Kidney-bean or coffee-bean shaped.
• Metabolism: Aerobic.
• Key enzyme: Oxidase-positive.
• Culture: Grow on chocolate agar. For selective growth from non-sterile sites (e.g., genital), use Thayer-Martin agar (chocolate agar with Vancomycin, Polymyxin, and Nystatin - “VPN”).
• Virulence Factor (shared): Pili for attachment, with high antigenic variation. t IgA protease cleaves secretory IgA.

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Neisseria gonorrhoeae (“Gonococcus”)

• Key Differentiator:
  • No polysaccharide capsule. t
  • Ferments glucose only. (Mnemonic: Gonococcus = Glucose).
  • No vaccine due to high antigenic variation of pili.
• Transmission: Sexual contact, perinatal.
• Clinical Features
  • Males:
    • Urethritis: Dysuria, copious purulent urethral discharge (thick, yellow-green).
    • Epididymitis: Unilateral testicular pain, swelling, and tenderness.
  • Females:
    • Asymptomatic: Up to 50–80% of infected females exhibit no symptoms.
    • Cervicitis: Mucopurulent endocervical discharge, postcoital bleeding, dysuria, and a friable cervix (bleeds easily on contact).
  • Extragenital:
    • Pharyngitis: Sore throat, pharyngeal erythema/exudate (often asymptomatic).
    • Proctitis: Tenesmus, rectal pain, purulent discharge, bleeding.
    • Disseminated Gonococcal Infection (DGI):
      • Triad: Tenosynovitis (asymmetric), migratory polyarthralgias, and dermatitis (painless pustular or petechial rash on distal extremities).
      • Septic Arthritis: Purulent monoarticular/oligoarticular arthritis (knee most common), joint swelling, limited ROM.
• Diagnosis: NAAT (Nucleic Acid Amplification Test) is the gold standard.
• Treatment: Ceftriaxone. Always co-treat for Chlamydia trachomatis (empirically with doxycycline or azithromycin), as co-infection is common.

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Neisseria meningitidis (“Meningococcus”)

• Key Differentiator:
  • Polysaccharide capsule is major virulence factor (antiphagocytic).
  • Ferments glucose AND maltose. (Mnemonic: Meningococcus = Maltose).
  • Vaccine available (targets capsular polysaccharide).
• Transmission: Respiratory droplets. High-risk in close quarters (dorms, military barracks).
• Pathophysiology: Colonizes nasopharynx -> invades bloodstream -> meningitis and/or meningococcemia. Septic shock is driven by outer membrane lipooligosaccharide (LOS) endotoxin. t
• Clinical Features:
  • Meningitis: High fever, headache, nuchal rigidity, photophobia.
  • Meningococcemia: Sepsis, petechial/purpuric rash (can progress to purpura fulminans), DIC.
  • Waterhouse-Friderichsen syndrome
    • Mechanism: Severe bacterial infection → endotoxic shock → Disseminated Intravascular Coagulation (DIC) → bilateral adrenal hemorrhage & infarction → adrenal crisis.
    • Clinical: Septic shock, petechial rash (purpura fulminans), DIC. t
• Diagnosis: Lumbar puncture (LP) shows CSF with ↑ neutrophils, ↑ protein, ↓ glucose. Gram stain of CSF. Blood cultures.
• Treatment: Ceftriaxone or Penicillin G.
• Prophylaxis:
  • For close contacts: Rifampin, ciprofloxacin, or ceftriaxone. t
    • Goal of prophylaxis is to eradicate nasopharyngeal carriage of the bacteria to prevent it from invading the bloodstream or spreading to others.
    • Rifampin can penetrate extremely well into body fluids and tissues, specifically saliva, tears, and nasopharyngeal secretions. Hence its side effect: orange/red discoloration of body fluids
  • Vaccine: Conjugate vaccine against serotypes A, C, Y, W-135. Separate vaccine for serotype B.