A 28-year-old woman presents with a 3-day history of dysuria, urethral discharge, and lower abdominal pain. On examination, she is afebrile; cervical examination reveals mucopurulent discharge. Gram stain of urethral secretions shows intracellular Gram-negative diplococci within polymorphonuclear leukocytes. She reports a new sexual partner 1 week ago. Which of the following statements about the causative organism is most accurate?

Question

Accepted Answer

C. It produces IgA protease and exhibits antigenic variation of pili, allowing immune evasion and recurrent infection. ## Clinical Diagnosis

**Key Point:** The clinical presentation of acute urethritis with mucopurulent cervical discharge and intracellular Gram-negative diplococci in PMNs is diagnostic of *Neisseria gonorrhoeae* (gonorrhea).

## Pathogenic Mechanisms of *N. gonorrhoeae*

**High-Yield:** *N. gonorrhoeae* employs two major immune evasion strategies:

1. **IgA Protease Production:** The organism secretes an IgA1 protease that cleaves IgA antibodies at the hinge region, inactivating the primary mucosal defense. This is a hallmark virulence factor shared with *N. meningitidis*.

2. **Antigenic Variation of Pili:** The organism undergoes high-frequency phase and antigenic variation in pilin genes (via recombination and mutation), allowing it to change its surface pili antigens and evade antibody recognition. This is why repeated infections are common and vaccine development is challenging.

**Clinical Pearl:** These mechanisms explain why gonorrhea can cause recurrent infections even after treatment and why natural immunity does not develop.

## Comparison of *N. gonorrhoeae* vs. *N. meningitidis*

| Feature | *N. gonorrhoeae* | *N. meningitidis* |
| --- | --- | --- |
| **Primary Site** | Urogenital tract | Nasopharynx |
| **IgA Protease** | Yes | Yes |
| **Pili Variation** | **Extensive (antigenic)** | Limited |
| **Glucose Fermentation** | Yes (only) | Yes |
| **Maltose Fermentation** | No | **Yes** |
| **Capsule Type** | Lipooligosaccharide (LOS) | Polysaccharide (sialic acid) |
| **Vaccine Availability** | None effective | MenACWY, MenB |

**Mnemonic: GONO-VARIATE** — *Gonorrhoeae* exhibits **Antigenic VARIATion** of pili, unlike meningococcus.

## Why Recurrent Infection Occurs

1. IgA protease neutralizes local IgA response.
2. Pilin antigenic variation allows the organism to present new epitopes.
3. No durable humoral or cellular immunity develops.
4. Reinfection is possible even after successful treatment.

Answer

A. It produces a lipopolysaccharide with a sialic acid capsule that is identical to the polysaccharide capsule of *N. meningitidis*

Answer

B. It is an obligate intracellular pathogen that requires special transport media and grows only on chocolate agar supplemented with vancomycin

Answer

D. It ferments both glucose and maltose, distinguishing it from the meningococcal species

Explanation

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