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XLD agar - xylose lysine deoxycholate agar - is a selective growth medium used in the isolation of Salmonella and Shigella species from clinical samples and from food. Most gut bacteria can ferment xylose to produce acid; shigella species cannot do this. Salmonellas metabolise lysine to produce hydrogen sulfide, which leads to the formation of black colonies.It has a pH of approximately 7.4.
XLD agar contains:
| Yeast extract | 3g/l |
| L-Lysine | 5g/l |
| Xylose | 3.75g/l |
| Lactose | 7.5g/l |
| Sucrose | 7.5g/l |
| Sodium deoxycholate | 1g/l |
| Sodium chloride | 5g/l |
| Sodium thiosulfate | 6.8g/l |
| Ferric ammonium citrate | 0.8mg/l |
| Phenol red | 0.08g/l |
| Agar | 12.5g/l |
"XLD agar"