Ashdown's medium is a selective culture medium for the isolation and characterisation of ''

Burkholderia pseudomallei ''Burkholderia pseudomallei'' (also known as ''Pseudomonas pseudomallei'') is a Gram-negative, bipolar, aerobic, motile rod-shaped bacterium. It is a soil-dwelling bacterium endemic in tropical and subtropical regions worldwide, particularly in ...

'' (the bacterium that causes

melioidosis Melioidosis is an infectious disease caused by a gram-negative bacterium called ''Burkholderia pseudomallei''. Most people exposed to ''B. pseudomallei'' experience no symptoms, but complications can range from fever and skin changes to pneumon ...

). 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 is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked-eye examination, microbiological investigation of respiratory infections, and Cytopathology, cytological ...

) as well as to produce the characteristic morphology of ''B. pseudomallei''. The medium contains

crystal violet Crystal violet or gentian violet, also known as methyl violet 10B or hexamethyl pararosaniline chloride, is a triphenylmethane, triarylmethane dye used as a histological stain and in Gram staining, Gram's method of classifying bacteria. Crystal ...

and

gentamicin Gentamicin is an aminoglycoside antibiotic used to treat several types of bacterial infections. This may include bone infections, endocarditis, pelvic inflammatory disease, meningitis, pneumonia, urinary tract infections, and sepsis amo ...

as selective agents to suppress the growth of other bacteria. Colonies of ''B. pseudomallei'' also take up

neutral red Neutral red (toluylene red, Basic Red 5, or C.I. 50040) 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 stain ...

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 , vauthors=Phetsouvanh R, Phongmany S, Newton P , 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 , issue=4, display-authors=etal, doi-access=free

References

Microbiological media