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MacConkey Agar

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MacConkey Agar


MacConkey agar is a selective and differential media used for the isolation and differentiation of non-fastidious gram-negative rods, particularly members of the family Enterobacteriaceae .

Composition



MacConkey agar is used for the isolation of gram-negative enteric bacteria and the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria. Pancreatic digest of gelatin and peptones (meat and casein) provide the essential nutrients, vitamins and nitrogenous factors required for growth of microorganisms. Lactose monohydrate is the fermentable source of carbohydrate. The selective action of this medium is attributed to crystal violet and bile salts, which are inhibitory to most species of gram-positive bacteria. Sodium chloride maintains the osmotic balance in the medium. 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. Agar is the solidifying agent.

Uses of MacConkey Agar
1.    MacConkey agar is used for the isolation of gram-negative enteric bacteria.
2.    It is used in the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria.
3.    It is used for the isolation of coliforms and intestinal pathogens in water, dairy products and biological specimens.
Preparation 
1.    Suspend 49.53 grams of dehydrated medium in 1000 ml purified/distilled water.
2.    Heat to boiling to dissolve the medium completely.
3.    Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. 
4.    Cool to 45-50°C.
5.    Mix well before pouring into sterile Petri plates.
Prepare culture
The specimen streaking on macconkey agar.Incubation 37c 18-24h

Image result for mannitol salt agar strin
Result Interpretation

Lactose fermenting strains grow as red or pink and may be surrounded by a zone of acid precipitated bile. The red colour is due to production of acid from lactose, absorption of neutral red and a subsequent colour change of the dye when the pH of medium falls below 6.8.

Lactose non-fermenting strains, such as Shigella and Salmonella are colourless and transparent and typically do not alter appearance of the medium. Yersinia enterocolitica may appear as small, non-lactose fermenting colonies after incubation at room temperature.

References
http://www.time2026end.com/

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