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. IgA protease cleaves secretory IgA.
• Neisseria gonorrhoeae (“Gonococcus”)
  • Key Differentiator:
    • No polysaccharide capsule.
    • Ferments glucose only. (Mnemonic: Gonococcus = Glucose).
    • No vaccine due to high antigenic variation of pili.
  • Transmission: Sexual contact, perinatal.
  • Clinical Features:
    • Men: Urethritis (purulent discharge), prostatitis, epididymitis.
    • Women: Often asymptomatic. Can cause cervicitis, Pelvic Inflammatory Disease (PID) → infertility, ectopic pregnancy. Fitz-Hugh-Curtis syndrome (perihepatitis, “violin-string” adhesions).
    • Both: Pharyngitis, proctitis.
    • Disseminated Gonococcal Infection (DGI): Classic triad of polyarthralgia, tenosynovitis, and dermatitis (pustules on an erythematous base). Can also cause septic arthritis (purulent, typically affects a single joint like the knee).
    • Neonates: Ophthalmia neonatorum (purulent conjunctivitis) within 2-5 days of birth. Prevented with erythromycin ointment at birth.
  • 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.
• 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.
  • Clinical Features:
    • Meningitis: High fever, headache, nuchal rigidity, photophobia.
    • Meningococcemia: Sepsis, petechial/purpuric rash (can progress to purpura fulminans), DIC.
    • Waterhouse-Friderichsen syndrome: Catastrophic complication of meningococcemia. Characterized by bilateral adrenal hemorrhage, leading to acute adrenal insufficiency, shock, and death.
  • 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.
    • Vaccine: Conjugate vaccine against serotypes A, C, Y, W-135. Separate vaccine for serotype B.