Xylose Lysine Agar Base
XL (Xylose Lysine) Agar Base is used for the isolation and differentiation of Gram-negative enteric bacteria. In this medium, Yeast Extract provides the nitrogenous sources and carbohydrates required for bacterial growth. Sodium Chloride supplies electrolytes and maintains the osmotic equilibrium. Xylose, Lactose and Sucrose are the fermentable carbohydrates, being the former metabolized by most enteric bacteria except for Shigella and Providencia spp. Upon Xylose depletion, Salmonella (but not non-pathogen xylose fermenters) decarboxylates L-Lysine and reverts the pH acidification due to carbohydrate fermentation. Phenol Red serves as pH indicator. Agar is the gelifying agent.
Formulation g/L Yeast Extract 3.00 L-Lysine 5.00 Lactose 7.50 Sucrose 7.50 Xylose 3.5 Sodium Chloride 5.00 Phenol Red 0.08 Agar 13.50 Total g/L
Final pH ( at 25°C) 7.4±0.2
Directions
Suspend 45.08 grams in 1000ml distilled water. Heat to boiling to dissolve the medium completely. Add brilliant green if desired. Sterilize by autoclaving at 118°C for 10 minutes. Cool to 50-55°C and aseptically add 20ml of sterile aqueous solution containing 34% sodium thiosulphate and 4% ferric ammonium citrate. Mix well and pour into sterile Petri plates.
Color and Clarity of prepared medium
Suspend 45.08 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Add brilliant green if desired. Sterilize by autoclaving at 118°C for 10 minutes. Cool to 50-55°C and aseptically add 20 ml of sterile aqueous solution containing 34% sodium thiosulphate and 4% ferric ammonium citrate. Mix well and pour into sterile Petri plates.
| Formulation | g/L |
| Yeast Extract | 3.00 |
| L-Lysine | 5.00 |
| Lactose | 7.50 |
| Sucrose | 7.50 |
| Xylose | 3.5 |
| Sodium Chloride | 5.00 |
| Phenol Red | 0.08 |
| Agar | 13.50 |
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