Absolutely! Here comes a clean, no-external-links, laboratory-ready specification for CLED Agar… with a tiny sprinkle of personality.
🧪 CLED Agar (Cystine–Lactose–Electrolyte-Deficient)
Created especially for clinical microbiology and urine diagnostics. The medium behaves like a detective who blocks the noisy troublemakers (swarming Proteus) while helping the quiet pathogens reveal their true colors.
✅ Purpose
- Isolation, enumeration, and differentiation of urinary pathogens from urine samples
- Prevents Proteus species from swarming
- Encourages lactose fermenters to show off (yellow colonies), while non-fermenters brood in blue-green silence
🎨 Colony Appearance
| Organism Type | Typical Colony Reaction |
|---|---|
| Lactose fermenters (E. coli, etc.) | Yellow colonies |
| Non-lactose fermenters (Proteus, Pseudomonas) | Blue/green colonies |
| Cystine-dependent coliforms | Enhanced growth due to cystine |
🧫 Typical Composition per Liter
Values may vary slightly by manufacturer, but this gives the common standard:
| Ingredient | Amount |
|---|---|
| Enzymatic digest of gelatine / Casein peptone | 4.0 g |
| Lactose | 10.0 g |
| L-Cystine | 0.128 g |
| Bromothymol blue | 0.02 g |
| Agar | ~14.0 g |
| Electrolyte-controlling agents | Present to suppress swarming |
| Final pH | 7.3 ± 0.2 at 25 °C |
🔍 Key Features
- Electrolyte-deficient: suppresses Proteus swarming
- Differential: lactose fermentation shown through pH-based color changes
- Supports cystine-dependent organisms
- Suitable for colony counts and morphological differentiation
🔬 Preparation Guidelines
- Suspend medium in distilled water and heat to dissolve
- Sterilize at 121 °C for ~15 minutes
- Cool to ~50 °C, pour plates
- Keep protected from excessive heat and light (indicator stability)
🌡 Incubation
- 35–37 °C for 18–24 hours (a bit longer if needed for slower pathogens)
- Ambient atmosphere; no CO₂ requirement
🚫 Limitations
Like any medium, CLED has quirks:
- Some fastidious organisms (e.g., Haemophilus, Neisseria) sulk and do not grow well
- Confirm identities biochemically; color alone never wins the case
- Prolonged incubation may blur color reactions
📌 Quick Summary
CLED Agar =
Cystine to support picky bacteria + Lactose for fermentation testing + Electrolyte-Deficiency to stop Proteus from throwing a rave party.
