MacConkey agar
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MacConkey Agar is a selective culture medium for the isolation of gram-negative bacteria such as salmonella , shigella and coliform bacteria in faeces , food , sewage and other habitats . At the same time, it is a differential medium : the colonies of organisms such as Escherichia coli , which can break down lactose fermentatively (lactose-positive), turn red; other gram-negative organisms remain colorless.
The recipe originally published in 1901 by the British microbiologist Alfred Theodore MacConkey (1861–1931) has now been modified.
Mode of action
The bile salts and crystal violet contained in MacConkey agar as inhibitors largely inhibit Gram-positive bacteria . Also serves lactose together with the pH - indicator neutral red to detect the lactose degradation. Lactose-positive bacteria show up as red colonies, E. coli colonies in particular also show a cloudy halo, which is caused by bile acids that precipitate due to the pH decrease (acid formation from lactose) .
Typical composition
The nutrient medium usually consists of (data in grams per liter ):
- Peptone from gelatin 17.0
- Peptone from casein and meat 3.0
- Table salt 5.0
- Lactose 10.0
- Bile salt mixture 1.5
- Neutral red 0.03
- Crystal violet 0.001
- Agar-agar 13.5
See also
- Blood agar
- Cetrimide agar
- CLED agar
- Endo agar
- Eosin Methylene Blue
- Mannitol salt agar
- Muller-Hinton agar
- Sabouraud Dextrose Agar
Web links
Individual evidence
- ↑ a b Technical information MacCONKEY agar from Carl Roth, accessed on January 5, 2015.