Ashdown's medium
Encyclopedia
Ashdown's medium is a selective culture medium for the isolation and characterisation of Burkholderia pseudomallei
Burkholderia pseudomallei
Burkholderia pseudomallei is a Gram-negative, bipolar, aerobic, motile rod-shaped bacterium. It infects humans and animals and causes the disease melioidosis. It is also capable of infecting plants....

(the bacterium that causes melioidosis
Melioidosis
Melioidosis is an infectious disease caused by a Gram-negative bacterium, Burkholderia pseudomallei, found in soil and water. It is of public health importance in endemic areas, particularly in Thailand and northern Australia. It exists in acute and chronic forms. Symptoms may include pain in...

).

Ashdown's medium was first described by LR Ashdown in 1979.
It is used for the selective isolation of B. pseudomallei from clinical specimens taken from non-sterile sites (e.g., sputum
Sputum
Sputum is mucus that is coughed up from the lower airways. It is usually used for microbiological investigations of respiratory infections....

) as well as to produce the characteristic morphology of B. pseudomallei.

The medium contains crystal violet
Crystal violet
Crystal violet or Gentian violet is a triarylmethane dye. The dye is used as a histological stain and in Gram’s method of classifying bacteria. Crystal violet has antibacterial, antifungal, and anthelmintic properties and was formerly important as a topical antiseptic...

 and gentamicin
Gentamicin
Gentamicin is an aminoglycoside antibiotic, used to treat many types of bacterial infections, particularly those caused by Gram-negative organisms. However, gentamicin is not used for Neisseria gonorrhoeae, Neisseria meningitidis or Legionella pneumophila...

 as selective agents to suppress the growth of other bacteria. Colonies of B. pseudomallei also take up neutral red
Neutral red
Neutral Red is a eurhodin dye used for staining in histology. It stains lysosomes red. It is used as a general stain in histology, as a counterstain in combination with other dyes, and for many staining methods. Together with Janus Green B, it is used to stain embryonal tissues and supravital...

which is present in the medium, and this further helps to distinguish it from other bacteria. Gentamicin slightly inhibits the growth of B. pseudomallei and so specimens inoculated onto Ashdown's agar needs to be incubated for a minimum of 96 hours instead of 48 hours. The medium is also enriched with 4% glycerol, which is required by some strains of B. pseudomallei to grow. B. pseudomallei usually produces flat wrinkled purple colonies on Ashdown's agar.

Ashdown's medium has the advantage of being extremely cheap to produce: the cost of each plate is only US$0.04.
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