Question 1: A patient presents with a history of watery diarrhea and vomiting. The pathogen exhibited darting motility. Which is the best selective media for the involved pathogen?
- A. Potassium Tellurite Agar
- B. Cetrimide agar
- C. TCBS (Correct Answer)
- D. Nutrient media
Explanation: ***Correct: TCBS***
- **Thiosulfate Citrate Bile Salts Sucrose (TCBS) agar** is the most widely used selective medium for isolating *Vibrio cholerae* and other *Vibrio* species from clinical and environmental samples
- The clinical presentation of **watery diarrhea and vomiting** with **darting motility** is characteristic of *Vibrio cholerae*
- *Vibrio cholerae* ferments **sucrose** in TCBS medium, producing **yellow colonies**, contrasting with the blue-green colonies of non-sucrose fermenters like *Vibrio parahaemolyticus*
- The medium contains **bile salts** that inhibit most Gram-positive bacteria while allowing Vibrio species to grow
*Incorrect: Nutrient media*
- Nutrient media is a **general-purpose** medium that supports the growth of a wide variety of non-fastidious organisms, making it **non-selective** for *Vibrio*
- It lacks the inhibitory agents (bile salts) and specific markers (sucrose) necessary for selective isolation and differentiation of *Vibrio* species
*Incorrect: Cetrimide agar*
- This medium is specifically selective for **Pseudomonas aeruginosa**, as cetrimide (a quaternary ammonium compound) inhibits the growth of most other bacteria
- *Vibrio cholerae* would likely be inhibited or overgrown by other organisms on this medium, making it unsuitable for isolation
*Incorrect: Potassium Tellurite Agar*
- Potassium Tellurite Agar (McLeod's medium) is a selective medium primarily used for the isolation of **Corynebacterium diphtheriae**
- The tellurite salt inhibits most other respiratory flora but does not specifically enhance or select for the growth of *Vibrio* species