CRITERION™ MACCONKEY AGAR

Cat. no. C6130 CRITERION™ MacConkey Agar 105gm
Cat. no. C6131 CRITERION™ MacConkey Agar 500gm
Cat. no. C6132 CRITERION™ MacConkey Agar 2kg
Cat. no. C6133 CRITERION™ MacConkey Agar 10kg
Cat. no. C6134 CRITERION™ MacConkey Agar 50kg

INTENDED USE

Hardy Diagnostics CRITERION™ MacConkey Agar is recommended for use as a selective and differential medium for the isolation of gram-negative bacilli (including coliform organisms and enteric pathogens), on the basis of lactose-fermentation.

This dehydrated culture medium is a raw material intended to be used in the making of prepared media products, which will require further processing, additional ingredients, or supplements.

SUMMARY

MacConkey Agar is a modification of Neutral Red Bile Salt Agar developed by MacConkey. It was one of the earliest culture media for the cultivation and identification of enteric organisms.(5) It has also been used in the isolation of pathogens from foods and coliforms in water samples.(8,9) The MacConkey Agar formulation presently in use is a modification of the original. In addition to containing sodium chloride, the modified formula has a lowered agar content and an adjusted concentration of bile salts and neutral red. 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 (Salmonella spp. and Shigellaspp.) develop into transparent, colorless colonies with no precipitated zone.

Peptones are incorporated into MacConkey Agar to provide amino acids and nitrogenous compounds. Sodium chloride is present to maintain osmotic equilibrium. Lactose is added as a possible carbon source for energy, and the acids produced from this activity precipitate out the bile salts. Bile salts and crystal violet are added to inhibit the growth of most gram-positive organisms.

FORMULA

Gram weight per liter: 50.0gm/L
Peptone 17.0gm
Lactose 10.0gm
Sodium Chloride 5.0gm
Bile Salts No. 3 1.5gm
Proteose Peptone 3.0gm
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 AND SHELF LIFE

Store the sealed bottle(s) containing culture medium at 2-30ºC. Dehydrated culture medium is very hygroscopic. Keep lid tightly sealed. Protect dehydrated culture media from moisture and light. The dehydrated culture media should be discarded if it is not free-flowing or if the color has changed from its original light pinkish-beige.

Store the prepared culture media in plates at 2-8ºC.

PRECAUTIONS

METHOD OF PREPARATION FOR DEHYDRATED CULTURE MEDIA

1. Suspend 52.49gm of the dehydrated culture media in 1 liter of distilled or deionized water.

2. Heat to boiling and mix to dissolve completely.

3. Sterilize in the autoclave at 121ºC. for 15 minutes. Avoid overheating.

4. Cool to 50-55ºC. and dispense approximately 20ml into sterile petri dishes.

PROCEDURE AND INTERPRETATION OF RESULTS

For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. G35.

LIMITATIONS

The concentration of bile salts in MacConkey Agar is relatively low in comparison with other enteric plating media. The parallel use of more selective media for gram-negative enterics, such as HE or XLD is recommended in order to increase the chances of pathogen isolation.

Some strains of Proteus may swarm on this medium.

Serial inoculation may be required to assure adequate isolation of mixed flora samples.

MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as autoclaves, incinerators, incubators, tubes, bottles, petri dishes, etc., are not provided.

QUALITY CONTROL

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

User Quality Control

PHYSICAL APPEARANCE

CRITERION™ MacConkey Agar powder should appear homogeneous, free-flowing, and light pinkish-beige in color. The prepared media should appear translucent, and pink in color.

REFERENCES

1. Anderson, N.L., et al. Cumitech 3B; Quality Systems in the Clinical Microbiology Laboratory, Coordinating ed., A.S. Weissfeld. American Society for Microbiology, Washington, D.C.

2. Versalovic, J., et al. Manual of Clinical Microbiology. American Society for Microbiology, Washington, D.C.

3. Tille, P., et al. Bailey and Scott's Diagnostic Microbiology, C.V. Mosby Company, St. Louis, MO.

4. Isenberg, H.D. Clinical Microbiology Procedures Handbook, Vol. I, II & III. American Society for Microbiology, Washington, D.C.

5. MacConkey, A.T. 1905. Lactose-fermenting bacteria in faeces. J. Hyg.; 5:333-379.

6. MacFaddin, J.F. 1985. Media for Isolation, Cultivation, Identification, Maintenance of Bacteria, Vol. I. Williams & Wilkins, Baltimore, MD.

7. Quality Assurance for Commercially Prepared Microbiological Culture Media, M22. Clinical and Laboratory Standards Institute (CLSI - formerly NCCLS), Wayne, PA.

8. American Public Health Association. Standard Methods for the Examination of Dairy Products, APHA, Washington, D.C.

10. United States Pharmacopoeia and National Formulary (USP-NF). Rockville, MD: United States Pharmacopeial Convention.


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

060616gr