MacConkey agar, usp

Cat. no. G35 MacConkey Agar, USP, 15x100mm Plate, 18ml 10 plates/bag
Cat. no. G35BX MacConkey Agar, USP, 15x100mm Plate, 18ml 100 plates/box
Cat. no. P47 MacConkey Agar, USP, Contact Plate, 15ml 10 plates/bag


Hardy Diagnostics MacConkey Agar, USP is recommended for use as a selective and differential medium for the isolation of gram-negative bacilli on the basis of lactose fermentation. The U.S. Pharmacopeia National Formulary <61> describes the use of MacConkey Agar for growth promotion of specified microorganisms in the microbiological examination of nonsterile products.(1)

This product is not intended to be used for the diagnosis of human disease.


MacConkey Agar, USP is prepared according to the U.S. Pharmacopoeia <62> standard formula for MacConkey Agar.(1) MacConkey Agar, USP contains peptones, which provide amino acids and other nitrogenous compounds to promote microbial growth. Sodium chloride is present to maintain osmotic equilibrium. Lactose is added as a possible carbon source for energy. Bile salts and crystal violet are added to inhibit the growth of most gram-positive organisms.

Differentiation of enteric microorganisms is achieved by the combination of the neutral red indicator and lactose. Lactose-fermenting organisms form pink colonies surrounded by a zone of bile salt precipitation. Color change is due to the production of acid, which changes the neutral red pH indicator from colorless to red. Acid production is also responsible for the formation of bile salt precipitation. Non-lactose-fermenters, such as Salmonella spp. and Shigella spp., develop transparent, colorless colonies with no precipitated zone.


Ingredients per liter of deionized water:*

Pancreatic Digest of Gelatin 17.0gm
Lactose Monohydrate 10.0gm
Sodium Chloride 5.0gm
Peptones (meat and casein) 3.0gm
Bile Salts 1.5gm
Neutral Red 30.0mg
Crystal Violet 1.0mg
Agar 13.5gm

Final pH 7.1 +/- 0.2 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.


Storage: Upon receipt store at 2-8ºC. away from direct light. Media should not be used if there are any signs of deterioration (shrinking, cracking, or discoloration), contamination, or if the expiration date has passed. Product is light and temperature sensitive; protect from light, excessive heat, moisture, and freezing.


Catalog nos. G35 and G35BX

Catalog no. P47


Specimen Collection: Consult listed reference for information on specimen collection.(1)

Method of Use:
Consult listed reference for the correct inoculation procedure.(1) Prior to inoculation, the medium should be brought to room temperature. The U.S. Pharmacopeoa recommends subculturing from MacConkey Broth, USP (Cat. no. U125). Streak to obtain isolated colonies. Incubate aerobically at 30-35ºC. for 18 to 72 hours. Examine plates for colony morphology.

Contact Plate Method of Use:
Allow plates to warm to room temperature. Select a surface to test. Sample the surface by firmly pressing the agar against the test area, using the thumb and second finger to hold the plate and the first finger to press firmly and evenly on the base. The same amount of pressure should be used for each sample. Do not move the plate laterally, as this spreads contaminants across the agar surface. A rolling motion may be used when slightly curved surfaces are sampled. Areas to be assayed may by divided into grids or sections, and samples may be taken from specific areas within the divisions. Incubate aerobically at 30-35ºC. for 18 to 72 hours. Examine plates for colony morphology.


Following incubation, the MacConkey Agar, USP is examined for typical colony morphology. Well isolated colonies of lactose-fermenting bacteria, such as Escherichia coli, appear pink to red in color and are surrounded by a zone of bile salt precipitation. Non-lactose-fermenting colonies, such as Shigella spp. and Salmonella spp., appear transparent and colorless, with no zone of bile salt precipitation. Consult the listed reference for further procedures for identification of isolates.(1)



Standard microbiological supplies and equipment such as loops, swabs, applicator sticks, other culture media (Cat. no. U125), incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Escherichia coli
ATCC® 8739**
J 18 hrs 30-35°C Aerobic   Growth; pink to red colonies with bile
precipitate surrounding colonies
Pseudomonas aeruginosa
ATCC® 9027
J 18-24 hrs 30-35°C Aerobic   Growth; colorless colonies
Salmonella enterica
ATCC® 14028
J 18-24 hrs 30-35°C Aerobic   Growth; colorless colonies
Staphylococcus aureus
ATCC® 6538
B 72 hrs 30-35°C Aerobic   Inhibited
Proteus mirabilis
ATCC® 12453
A 24 hrs 35°C Aerobic   Growth; colorless colonies, no swarming
Escherichia coli
ATCC® 25922
A 24 hrs 35°C Aerobic   Growth; pink to red colonies with bile precipitate surrounding colonies
Enterococcus faecalis
ATCC® 29212
B 24 hrs 35°C Aerobic   Partial to complete inhibition

**Tested in accordance with USP <62>.(1)


Physical Appearance

MacConkey Agar, USP should appear transparent, slightly opalescent, and pink in color.


1. The Official Compendia of Standards. USP-NF. United States Pharmacopeial Convention, Rockville, MD.

ATCC is a registered trademark of the American Type Culture Collection.