CLED agar (cystine lactose electrolyte deficient medium) is a valuable non-inhibitory growth medium used in the isolation and differentiation of urinary organisms. Being electrolyte deficient, it prevents the swarming of Proteus species. Cystine promotes the formation of cystine-dependent dwarf colonies. Lactose fermenters produce yellow colonies on CLED agar; non-lactose fermenters appear blue. It has a pH of approximately 7.3. CLED agar contains:
| Peptone | 4g/l |
| 'Lab Lemco' powder | 3g/l |
| Tryptone | 4g/l |
| Lactose | 10g/l |
| L-Cystine | 128 mg/l |
| Bromothymol blue | 20 mg/l |
| Agar No. 1 | 15g/l |
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