MacConkey agar

MacConkey Agar is a selective and differential culture medium for bacteria. It is designed to selectively isolate Gram-negative and enteric (normally found in the intestinal tract) bacilli and differentiate them based on lactose fermentation.

Composition[edit | edit source]

MacConkey Agar contains lactose, bile salts, neutral red, crystal violet, and agar. The bile salts and crystal violet inhibit the growth of Gram-positive organisms which makes MacConkey Agar selective. Neutral red is a pH indicator that turns red at a pH below 6.8 and is colorless at any pH greater than 6.8. Lactose provides a source of fermentable carbohydrate, allowing for differentiation.

Uses[edit | edit source]

MacConkey Agar is used for the isolation of Gram-negative enteric bacteria. It is used in the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria. It is used in the detection and/or verification of E.coli in water, food, and dairy products.

Interpretation[edit | edit source]

On MacConkey Agar, colonies of lactose fermenting bacteria are brick-red and may be surrounded by a zone of precipitated bile. The red color is due to production of acid from lactose, absorption of neutral red and a subsequent color change of the pH indicator from colorless to red. Non-lactose fermenting bacteria form transparent, colorless colonies.

History[edit | edit source]

MacConkey Agar was developed in 20th century by Alfred Theodore MacConkey, an English bacteriologist. It was the first formulated solid differential media.

See also[edit | edit source]

MacConkey agar Resources
Need Help Finding a Doctor? Need help finding a doctor or specialist anywhere in the world? Explore our world directory. WikiMD's DocFinder can assist you in locating millions of physicians.	Medical Knowledge Access the latest research - Most recent articles Ongoing trials.