MACCONKEY AGAR

Cat. no. GA35 MacConkey Agar, 15x100mm Plate, 19ml
(reduced stacking ring)
10 plates/bag
Cat. no. Q63 MacConkey Agar, 20x150mm, 20ml Deep 20 tubes/box
Cat. no. J32 Blood Agar / MacConkey Agar, 15x100mm Biplate,
10ml/10ml
10 plates/bag
Cat. no. J32BX Blood Agar / MacConkey Agar, 15x100mm Biplate,
10ml/10ml
100 plates/box
Cat. no. J58 MacConkey Agar / EMB Agar, Levine, 15x100mm Biplate,
10ml/10ml
10 plates/bag
Cat. no. J62 Columbia CNA Agar / MacConkey Agar, 15x100mm Biplate,
10ml/10ml
10 plates/bag
Cat. no. J62BX Columbia CNA Agar / MacConkey Agar, 15x100mm Biplate,
10ml/10ml
100 plates/box
Cat. no. J85 Rose Agar / MacConkey Agar, 15x100mm Biplate,
10ml/10ml
10 plates/bag
Cat. no. J314 Cetrimide Selective Agar / MacConkey Agar / Vogel and Johnson Agar, 15x100mm Triplate, 7ml/section 10 plates/bag

INTENDED USE

Hardy Diagnostics 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.

Cat. no. J314 is not intended to be used for the diagnosis of human disease.

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 Shigella spp.) 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

Ingredients per liter of deionized water:*

Peptone 17.0gm
Lactose 10.0gm
Sodium Chloride 5.0gm
Proteose Peptone 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 AND SHELF LIFE

Storage: Upon receipt store at 2-8ºC. away from direct light (Cat. no. Q63 may be stored at 2-30°C). 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.

PRECAUTIONS

For Cat. nos. GA35, Q63, J32, J32BX, J36, J58, J62, J62BX, J85.

For Cat. no. J314

PROCEDURE

Specimen Collection: Consult listed references for information on specimen collection. (1-4) Infectious material should be submitted directly to the laboratory without delay and protected from excessive heat and cold. If there is to be a delay in processing, the specimen should be inoculated onto an appropriate transport media and refrigerated until inoculation.

For MacConkey Agar deeps (Cat. no. Q63), liquify the medium by heating the number of desired tubes in a boiling water bath (100°C.). Cool the medium to 45-50ºC. and aseptically pour the contents of each tube into separate sterile petri dishes. Allow the medium to solidify in plates for at least 30 minutes prior to use.

Method of Use: Allow plates to warm to room temperature. The agar surface should be dry before inoculating. Inoculate and streak the specimen as soon as possible after collection. If the specimen to be cultured is on a swab, roll the swab over a small area of the agar surface. Streak for isolation with a sterile loop. Incubate plates aerobically at 35-37ºC. for 18-24 hours. Protect from light. Examine plates for colonial morphology.

INTERPRETATION OF RESULTS

Following incubation, the MacConkey Agar is examined for typical colonial morphology. Well isolated colonies of lactose-fermenting bacteria 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 references for further procedures for identification of isolates. (1-4)

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 (Cat. no. G63) or XLD (Cat. no. G65) 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.

It is recommended that the medium in agar deeps be melted only once prior to use. Do no reheat tubes multiple times. Discard any unused liquified agar deeps if not immediately poured into plates.

MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as loops, other culture media, slides, microscopes, staining supplies, incinerators, and incubators, etc., as well as serological and biochemical reagents, 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
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
Enterococcus faecalis
ATCC® 29212
B 24hr 35°C Aerobic Partial to complete inhibition

User Quality Control

Physical Appearance

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

E. coli growing on MacConkey Agar

Escherichia coli ATCC® 25922) colonies growing on MacConkey Agar. Incubated aerobically for 24 hours at 35ºC.

P. mirabilis growing on MacConkey Agar

Proteus mirabilis (ATCC® 12453) colonies growing on MacConkey Agar. Incubated aerobically for 24 hours at 35ºC.


S. typhimurium growing on MacConkey Agar

Salmonella enterica (ATCC® 14028) colonies growing on MacConkey Agar. Incubated aerobically for 24 hours at 35ºC.

E. faecalis inhibited on MacConkey Agar

Enterococcus faecalis (ATCC® 29212) growth inhibited on MacConkey Agar. Incubated aerobically for 24 hours at 35ºC.


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. Biochemical Tests for Identification of Medical Bacteria,, Lipincott Williams & Wilkins, Philadelphia, PA.

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.

9. American Public Health Association. Standard Methods for the Examination of Water and Wastewater, APHA, Washington, D.C.

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

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