Ashdown’s Agar- Composition, Principle, Preparation, Results, Uses


Ashdown’s agar is a selective and differential medium for the isolation and identification of Burkholderia pseudomallei, the causative agent of melioidosis. The medium was developed by Ashdown and colleagues in 1979 and has been widely used in areas where melioidosis is endemic.

The composition of Ashdown’s agar is as follows:

  • Ingredient: Peptone
  • Amount (g/L): 10.0
  • Ingredient: Yeast extract
  • Amount (g/L): 3.0
  • Ingredient: Sodium chloride
  • Amount (g/L): 5.0
  • Ingredient: Agar
  • Amount (g/L): 15.0
  • Ingredient: Glycerol
  • Amount (g/L): 40.0
  • Ingredient: Neutral red
  • Amount (g/L): 0.05
  • Ingredient: Crystal violet
  • Amount (g/L): 0.002
  • Ingredient: Gentamicin sulfate
  • Amount (g/L): 0.004

The medium contains crystal violet and gentamicin as selective agents to suppress the growth of other bacteria. Colonies of B. pseudomallei also take up neutral red which is present in the medium, and this further helps to distinguish it from other bacteria.

The medium is also enriched with 4% glycerol, which is required by some strains of B. pseudomallei to grow.

Source: Ashdown LR, Guard RW, Pitt TL. A selective medium for the isolation of Pseudomonas pseudomallei from clinical specimens. Pathology. 1979;11(4):293-300. Ashdown LR. An improved screening technique for isolation of Pseudomonas pseudomallei from clinical specimens. Pathology. 1985;17(4):599-601.