Sorbitol MacConkey Agar

//Sorbitol MacConkey Agar

Sorbitol MacConkey Agar

SKU: KM0010 Category:

Sorbitol MacConkey agar is a differential medium for the isolation of Escherichia coli 0157:H7 based on the formulation by Rappaport and Henig. It differs from other MacConkey mediums in that lactose has been replaced by sorbitol. As Escherichia coli 0157:H7 does not ferment sorbitol it produces pale translucent colonies whereas most other strains of Escherichia coli are sorbitol positive and produce pink colonies. Although it should be noted that colonies that are sorbitol positive can revert and possibly be mistaken as sorbitol negative. Tryptone and meat peptone provide the required carbon, nitrogen and vitamins. Sorbitol is a fermentable carbohydrate and neutral red is a pH indicator. Bile Salts no.3 and crystal violet are selective agents and together inhibit Gram-positive cocci. Sodium chloride maintains the osmotic balance. If required, the selectivity of the medium may be increased by the addition of cefixime (0.05mg/L) and potassium tellurite (2.5mg/L).

Related Supplements :
LS0013 Escherichia coli 0157 Selective Supplement

Additional Information

Shelf Life (days)

Storage Temp (°C)

Dehydrated Medium Appearance

Prepared Medium Appearance

Dehydrated Medium Colour

Prepared Medium Colour

Dehydrated PH

Prepared PH

Product Description

Organisms Ref. No Result
Escherichia coli O157 NCTC 12900 Growth, colourless colonies
Escherichia coli NCTC 12241 Inhibited
Staphylococcus aureus NCTC 12981 Inhibited



Tryptone 17.0
Meat peptone 3.0
Sorbitol 10.0
Bile Salts No.3 1.5
Sodium chloride 5.0
Neutral red 0.03
Crystal violet 0.001
Agar 12.0
Total 48.5
*Adjusted/supplemented as required to meet performance requirements


Suspend 48.5g of the medium in one litre of deionised / purified water. Allow the medium to soak whilst mixing for 10 minutes. Heat with frequent agitation and boil for one minute to completely dissolve the medium. Sterilise at 121°C for 15 minutes. Cool to 45-50°C. If required add two vials of E. coli O157 selective supplement (LS0013) at this point, mix well and aseptically dispense into appropriate sterile containers.