MacConkey agar

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MacConkey agar is an indicator, selective and differential bacterial culture medium designed to isolate Gram-negative and enteric (usually found in the intestinal tract) bacillus and differentiate it based on lactose fermentation. Crystals violet and bile salts inhibit the growth of gram-positive organisms that allow for the selection and isolation of gram-negative bacteria. Enteric bacteria that have lactose fermentability can be detected using lactose carbohydrates, and a neutral red pH indicator.

Video MacConkey agar

Contents

It contains bile salts (to inhibit most Gram-positive bacteria), purple crystalline dyes (which also inhibit certain Gram-positive bacteria), a neutral red dye (which changes color to pink if microbes ferment lactose).

Compose:

• Peptone - 17 g
• Peptone Protease - 3 g
• Lactose - 10 g
• Garam empedu - 1.5 g
• Sodium chloride - 5 g
• Merah netral - 0.03 g
• Crystals - 0.001 g
• Agar - 13.5 g
• Air - tambahkan 1 liter; sesame pH kc 7.1/- 0.2

There are many variations of MacConkey to depend on needs. If the spread or grazing of Proteus species is not required, sodium chloride is removed. Violet crystals at a concentration of 0.0001% (0.001 g per liter) are included when it is necessary to check whether Gram-positive bacteria are inhibited. MacConkey with sorbitol is used to isolate E. coli O157, enteric pathogens.

Maps MacConkey agar

History

The media was developed by Alfred Theodore MacConkey while working as a bacteriologist for the Royal Commission on Waste Disposal.

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Usage

Using a red neutral pH indicator, to distinguish Gram-negative bacteria that can ferment lactose (Lac) sugars from those that can not (Lac-) fermentation.

This medium is also known as "indicator media" and "low selective medium". The presence of bile salts inhibits the population of Proteus .

Lac positive

By utilizing lactose available in the medium, Lac bacteria such as Escherichia coli Enterobacter and Klebsiella will produce acids, which decrease the pH from agar to below 6 , 8 and produces a pink colony display. Bile salts settle in the environment around the colony, causing the medium surrounding the colony to become foggy.

Lac negative

Non-lactose bacterial fermentation such as Salmonella , Proteus species, Yersinia , Pseudomonas aeruginosa and Shigella .

Slow

Some organisms lactose or ferment lactose slowly, and are sometimes included in their own categories. These include Serratia and Citrobacter .

Molecular colonies

Some organisms, especially Klebsiella and , produce mucoid colonies that look very moist and sticky. This phenomenon occurs because the organism produces capsules, most of which are made from lactose sugar in agar.

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Variant

The variant, sorbitol-MacConkey agar, (with the addition of additional selective agents) may be helpful in isolation and differentiation of E. coli serotype E. coli O157: H7, in the presence of a colorless circular colony which is a non-sorbitol that fermentes.

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See also

• R2a order
• MRS agar (a culture medium designed to grow Gram-positive bacteria and differentiate it for lactose fermentation).

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References

Source of the article : Wikipedia