Ashdown's medium

Ashdown's medium is a selective culture medium for the isolation and characterisation of "Burkholderia pseudomallei" (the bacterium that causes melioidosis).

Ashdown's medium was first described by LR Ashdown in 1979. [cite journal
author=Ashdown LR
title=An improved screening technique for isolation of "Pseudomonas pseudomallei" from clinical specimens
journal=Pathology
year=1979
volume=11
pages=293–7
pmid=460953
doi=10.3109/00313027909061954] It is used for the selective isolation of "B. pseudomallei" from clinical specimens taken from non-sterile sites (e.g., sputum) [cite journal
author=Peacock SJ, Chieng G, Cheng AC, "et al."
title=Comparison of Ashdown's medium, "Burkholderia cepacia" medium, and "Burkholderia pseudomallei" selective agar for clinical isolation of "Burkholderia pseudomallei"
journal=J Clin Microbiol
year=2005
volume=43
pages=5359–61
doi=10.1128/JCM.43.10.5359-5361.2005] as well as to produce the characteristic morphology of "B. pseudomallei". [cite journal
author=Chantratita N, Wuthiekanun V, Boonbumrung K, "et al."
title=Biological relevance of colony morphology and phenotypic switching by "Burkholderia pseudomallei"
journal=J Bacteriol
year=2007
volume=189
pages=807–17
doi=10.1128/JB.01258-06]

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. 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. [cite journal
author=Phetsouvanh R, Phongmany S, Newton P, "et al."
title=Melioidosis and Pandora's box in the Lao People's Democratic Republic
journal=Clin Infect Dis
year=2001
volume=32
pages=653–4
pmid=11181133
doi=10.1086/318713]

References