MacConkey Agar No.3

//MacConkey Agar No.3

MacConkey Agar No.3

SKU: KM0027 Category:

MacConkey agar No. 3 is a selective medium primarily for the isolation of Enterobacteriacae from waters and sewage. This media differs from the original MacConkey formulation in that as well as bile salts, crystal violet has been included as an additional selective agent. This has the effect of inhibiting Gram-positive organisms.
The peptone acts as a nitrogen, carbon and vitamin source. Sodium chloride maintains osmotic balance. Lactose is a carbohydrate and during its fermentation causes a confined pH drop around the bacterial colony. This causes a colour change in the pH indicator, neutral red and bile precipitation.


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Dehydrated Medium Appearance

Prepared Medium Appearance

Dehydrated Medium Colour

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Prepared PH

Product Description

Organisms Ref. No Result
Escherichia coli NCTC 12241 Growth, pink / red colonies
Proteus mirabilis NCTC 10975 Growth, pale colonies
Salmonella typhimurium NCTC 12023 Growth, pale colonies
Enterococcus faecalis NCTC 12697 Inhibited



Peptone 20.0
Lactose 10.0
Bile salts no.3 1.5
Sodium chloride 5.0
Neutral red 0.03
Crystal violet 0.001
Agar 15.0
Total 51.5
*Adjusted/supplemented as required to meet performance requirements


Suspend 51.5g of the medium in one litre of deionised / purified water. Allow the medium to soak whilst mixing for 10 minutes. Sterilise at 121°C for 15 minutes with frequent stirring to completely dissolve the medium. Cool to 45-50°C and dispense into appropriate sterile containers.