Neisseria meningitidis Lecture Notes

Defining Characteristics

• Type: Gram-negative diplococcus
• Unique Trait: facultative intracellular
• Fermentation: Ferments both maltose and glucose
• Colonization: Nasopharynx
• Transmission: Via respiratory droplets
• Major Disease: Community-acquired bacterial meningitis
• Rare Syndrome: Waterhouse-Friedrichsen syndrome (discussed later)

Virulence Factors

1. IgA1 Protease

   • Cleaves mucosal IgA
   • Enhances adherence to mucous membranes
   • Important for immunology exams: relates to mucosal surfaces.

2. Polysaccharide Capsule

   • Prevents phagocytosis
   • Key fact for exams: High yield to know.
   • Associated with overwhelming post-splenectomy infection (OPSI).

3. Lipo-oligosaccharide Endotoxin

   • Induces IL-1 and TNF-alpha
   • Can lead to overwhelming sepsis.

4. Adhesins

   • Promote bacterial attachment
   • Prevent activation of lymphocytes.

Most Important Virulence Factor

• Polysaccharide Capsule:
  • Prevents phagocytosis
  • Critical for patients with splenectomy or functional asplenia due to risk of OPSI.

Understanding OPSI

• Opsonization Process:
  1. Bacteria tagged with IgG or C3b (opsonins).
  2. Splenic macrophages identify the tag and phagocytize bacteria.
• Risk Factor:
  • Patients without a spleen cannot effectively clear encapsulated bacteria, leading to infection.
  • Specific bacteria: Strep pneumoniae, H. influenzae, N. meningitidis.
• Mneumonic for the bacteria: "SHIN"
  • S = S pneumoniae
  • H = H influenzae
  • N = Neisseria meningitidis.

Associations & Memorization

• Memorization Tip: "Opsi-shin" relates to opsonins and illustrates the risk of overwhelming post-splenectomy infection.

Clinical Features of Meningitis

• Symptoms to watch for:
  • Fever
  • Headache
  • Photophobia
  • Nuchal rigidity
  • Altered mental status

Physical Exam Maneuvers

• Kernig's Sign: Flexion at the thigh and extension at the knee. Pain/unable to extend indicates a positive sign.
• Brudzinski's Sign: Neck flexion causes reflexive hip flexion due to tension in the meninges.

Waterhouse-Friedrichsen Syndrome

• Infection leads to hemorrhagic necrosis of adrenal glands.
• Can result in:
  • Disseminated Intravascular Coagulation (DIC)
  • Petechiae evolving into purpura.
• Clinical Presentation: Similar to Addison's disease.
  • If a meningitis patient has a petechial rash, consider Waterhouse-Friedrichsen syndrome as a complication.

Treatment Overview

• Main Treatments:
  • Third-generation cephalosporins
  • Rifampin

Conclusion

• Key points to understand: OPSI and Waterhouse-Friedrichsen syndrome.
• Mastering these concepts is crucial for understanding Neisseria meningitidis and its implications in clinical settings.