Neisseria Gonorrhoeae - USMLE Step 1

Jul 26, 2024

Neisseria Gonorrhoeae - USMLE Step 1

Introduction

  • High-yield topic for USMLE Step 1.
  • Medically important gram-negative cocci.
  • Forms coffee bean-like structures known as diplococci.
  • Non-spore-forming, catalase-positive, oxidase-positive.
  • Known for causing sexually transmitted disease gonorrhea.

Features of N. Gonorrhoeae

Morphology

  • Gram-negative organism.
  • Thin cell wall; does not retain crystal violet; counterstains with pinkish saffronene.
  • Appears as diplococci (pairs).
  • Facultatively intracellular.
  • Fastidious and grow inside cells.
  • Obligate aerobes (require oxygen).

Mobility

  • Capable of twitching motility.

Classification

  • Gram-negative cocci.
  • Two important species: N. gonorrhoeae and N. meningitidis.
    • N. gonorrhoeae: Responsible for gonorrhea.
    • N. meningitidis: Important for meningitis infection.

Transmission

  • Via unprotected sex, multiple partners, pregnancy, or blood transfusion.
  • Incidence is increasing globally.

Symptoms of Gonorrhea

  • Abdominal pain.
  • Discharge from penis and vagina.
  • Painful urination.

Pathology and Immune Response

Attachment and Immune Modulation

  • Pili and OMP2 proteins help in docking onto epithelial cells like urethra, cervix, rectum, and conjunctivitis.

Immune Evasion

  • Pili protect against phagocytosis by macrophages and dendritic cells.
  • Secretes IgA protease to cleave IgA antibodies.
  • Blocks complement system and suppresses Th1 and Th2 T cells.
  • Induces Th17 T cells leading to inflammation and neutrophil mobilization.
  • Influences neutrophils to become infested and eventually die, exacerbating infection.
  • Modifies surface adhesion proteins to prevent complement pathways.
  • Resists oxidative burst from macrophages and neutrophils.
  • Alters cytokine secretion to evade immune response.

Diagnosis

  • Isolated using Thayer-Martin media (modified chocolate agar with antibiotics).
  • PCR-based tests from urine for accurate and quick diagnosis.
  • Purulent discharge can be gram-stained to identify gram-negative diplococci.
  • ELISA-based methods for additional sensitivity.

Treatment

  • CDC recommends ceftriaxone injection (500 mg intramuscularly).
  • Rapid diagnosis and treatment are crucial.
  • Follow-up after 3-4 months to check for reinfection.
  • Variable antibiotic response based on ethnicity and geography.
  • Concern over increasing antibiotic resistance.

Summary

  • Overview of gonorrhea caused by N. gonorrhoeae.
  • Symptoms, diagnosis, and treatment discussed.
  • Emphasis on antibiotic resistance issues.

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