Neisseria meningitidis and Neisseria gonorrhoeae are both gram-negative diplococci, but they differ in several key biochemical properties. Which of the following is a distinguishing feature that separates N. meningitidis from N. gonorrhoeae?

Explanation

## Biochemical Differentiation of Neisseria Species **Key Point:** The carbohydrate fermentation pattern is the gold standard for differentiating N. meningitidis from N. gonorrhoeae in the laboratory. ### Carbohydrate Fermentation Patterns | Organism | Glucose | Maltose | Lactose | Sucrose | |----------|---------|---------|---------|----------| | **N. meningitidis** | + | **+** | − | − | | **N. gonorrhoeae** | + | **−** | − | − | | N. lactamica | + | + | **+** | − | **High-Yield:** Both organisms ferment **glucose only** (oxidatively, not fermentatively). The ability to ferment **maltose** is the key distinguishing feature: - **N. meningitidis:** Maltose-positive (ferments maltose) - **N. gonorrhoeae:** Maltose-negative (does not ferment maltose) ### Clinical Significance **Mnemonic:** **"Meningitis = Maltose"** — N. meningitidis ferments Maltose. ### Why This Matters 1. **Rapid identification:** Fermentation tests are quick and inexpensive 2. **Epidemiological tracking:** Helps confirm the causative agent in meningitis vs. urethritis 3. **Treatment implications:** Both require similar antibiotics, but clinical context differs ### Other Shared Features (Not Differentiating) - Both are oxidase-positive (gram-negative diplococci with oxidase enzyme) - Both produce IgA protease (virulence factor) - Both require selective media (Thayer-Martin or modified Thayer-Martin) - Both are fastidious organisms requiring enriched media **Clinical Pearl:** N. lactamica, a commensal of the nasopharynx, ferments glucose, maltose, AND lactose—making it the only Neisseria that ferments lactose. This helps differentiate it from the pathogenic species. [cite:Jawetz, Melnick & Adelberg's Medical Microbiology 28e Ch 13]