Which of the following media is selective and differential, used specifically for isolation of Vibrio species from clinical samples?

Explanation

## Selective and Differential Media for Vibrio **Key Point:** TCBS agar is the gold standard selective and differential medium for isolation of Vibrio species, particularly *Vibrio cholerae* and *Vibrio parahaemolyticus*. ### Composition and Function - **Selective components:** Thiosulfate, citrate, and bile salts inhibit gram-positive bacteria and most coliforms - **Differential component:** Sucrose fermentation produces yellow colonies for *V. cholerae* (sucrose-fermenting) and blue-green colonies for non-sucrose-fermenting vibrios - **pH:** Alkaline (pH 8.5), which favors vibrio growth ### Why TCBS is Preferred 1. Suppresses normal fecal flora effectively 2. Allows rapid identification based on colony color 3. High sensitivity and specificity for Vibrio isolation 4. Recommended by WHO for cholera surveillance **High-Yield:** *V. cholerae* produces **flat, yellow, mucoid colonies** (resembling a "fried egg") on TCBS, while non-O1/non-O139 strains produce **blue-green colonies**. **Mnemonic:** **TCBS = The Cholera Bacterium's Special** medium ### Comparison with Other Media | Medium | Type | Primary Use | Vibrio Isolation | |--------|------|-------------|------------------| | TCBS | Selective & Differential | Vibrio spp. | **Gold standard** | | MacConkey | Selective & Differential | Enterobacteriaceae | Poor (inhibits Vibrio) | | Blood agar | Enriched | General culture | Non-selective | | Chocolate agar | Enriched | Fastidious organisms | Non-selective | **Clinical Pearl:** In endemic areas, enrichment in alkaline peptone water (APW, pH 8.5) for 6–8 hours before plating on TCBS increases isolation rates of *V. cholerae* from stool samples.