Cat. no. G40 Mannitol Salt Agar (MSA), USP, 15x100mm Plate, 18ml 10 plates/bag
Cat. no. P98 Mannitol Salt Agar (MSA), USP, Contact Plate, 12ml 10 plates/bag


Hardy Diagnostics Mannitol Salt Agar (MSA), USP is recommended for use as a selective and differential medium for the isolation of pathogenic staphylococci. The medium complies with the harmonized European, U.S., and Japanese Pharmacopoeias for determining the microbial quality of non-sterile products.

These products are not intended to be used for the diagnosis of human disease.


Koch reported the use of a medium containing 7.5% sodium chloride as a selective agent for the isolation of staphylococci in 1942. The results were confirmed and improved by Chapman in 1945 by the addition of salt to Phenol Red Mannitol Agar, as Staphylococcus aureus usually ferments mannitol. Non-pathogenic staphylococci usually show less luxuriant growth on this medium after the incubation period.

A sodium chloride concentration of 7.5% is nearly ten times the usual concentration seen in most media. It serves to inhibit most organisms except staphylococci in mixed flora specimens. The beef extract and peptones supply the essential elements carbon, nitrogen, and sulfur. Mannitol is added to show fermentation capability of the organism. Acid production as the result of fermentation of this sugar results in the formation of colonies with a yellow zone. Those staphylococci that do not ferment mannitol show a purple or red zone around the colonies.

Mannitol Salt Agar (MSA) is recommended by the American Public Health Association for the enumeration of staphylococci in food and dairy products.(2,3) The medium is prepared according to the U.S. Pharmacopoiea Standard formula for Mannitol Salt Agar.(5)

MSA Contact Plates (Cat. no. P98) are to be used to test for contamination of surfaces by pathogenic staphylococci.


Ingredients per liter of deionized water:*

Sodium Chloride 75.0gm
Mannitol 10.0gm
Peptic Digest of Animal Tissue 5.0gm
Pancreatic Digest of Casein 5.0gm
Beef Extract 1.0gm
Phenol Red 0.025gm
Agar 15.0gm

Final pH 7.4 +/- 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 No. G40

Catalog No. P98


Prepare a sample using a 1:10 dilution of not less than 1.0gm of product to be examined as described in <61> and use 10mL or quantity corresponding to 1.0gm or 1.0mL to inoculate a suitable amount (main suitability of test method) of TSB, USP and homogenize. Incubate enrichment per <61>. Subculture TSB, USP enrichemnt to MSA, USP, and incubate at 30-35oC for 18-72 hours.

Method of Use, Contact Plates: Aseptically remove lid of contact plate. Gently place on area to be tested. Using a rolling motion, keep the plate in place, making sure all of the agar surface touches the testing area. Do not wipe or rub the contact plate on the surface being tested. Cover with the lid, and incubate and examine as described above.


The presence of S. aureus is indicated by the growth of yellow or white colonies surrounded by a yellow zone. Confirm colonies by identification tests.(2-5)


Most organisms other than staphylococci are inhibited by the high salt concentration found in Mannitol Salt Agar except for some halo-tolerant organisms such as Enterococcus faecalis.


Standard microbiological supplies and equipment such as loops, other culture media, swabs, applicator sticks, incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Staphylococcus aureus**
ATCC® 6538
J 18-72hr 30-35°C Aerobic Growth; yellow colonies and media at 18-24 hours
Staphylococcus aureus**
ATCC® 25923
A 24-48hrs 35°C Aerobic Growth; yellow colonies and media at 24-48 hours
Proteus mirabilis**
ATCC® 12453
B 24hrs 35°C Aerobic Partial to complete inhibition
Escherichia coli**
ATCC® 8739
A 18-72hrs 30-35°C Aerobic Partial to complete inhibition
** Tested in accordance with USP <62>.(4,5)


Physical Appearance

Mannitol Salt Agar (MSA), USP should appear clear, slightly opalescent, and pinkish-red in color.


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

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

3. APHA Technical Committee on Microbiological Methods for Foods. Compendium of Methods for the Microbiological Examination of Foods, APHA, Washington, D.C.

4. The Official Compendia of Standards. USP General Chapter <61> Microbiological Examination of Nonsterile Products: Microbial Enumeration Tests. USP-NF. United States Pharmacopeial Convention Inc., Rockville, MD.

5. The Official Compendia of Standards. USP General Chapter <62> Microbiological Examination of Nonsterile Products: Testsfor Specified Microorganisms. USP-NF. United States Pharmacopeial Convention Inc., Rockville, MD.

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