Mannitol Salt Medium

Mannitol salt agar is both a selective and differential media used for the isolation of pathogenic Staphylococci from mixed cultures. Mannitol Salt Agar (MSA) is recommended by the American Public Health Association for the enumeration of staphylococci in food and dairy products1,2. In 1942 Koch reported the use of a medium containing 7.5% sodium chloride as a selective agent for the isolation of staphylococci and improved by Chapman in 1945 by the addition of this salt concentration to Phenol Red Mannitol Agar, as Staphylococcus aureus usually ferments mannitol3. A sodium chloride, concentration of 7.5%, is nearly ten times the usual concentration seen in most media that inhibits most organisms except staphylococci in mixed flora specimens. Non-pathogenic staphylococci usually show less luxuriant growth on this medium after the incubation period. Mannitol show the fermentation capabilities of the organisms, the acid produced as the result of fermentation of Mannitol 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.

Product NameCatalog #Quantity
Mannitol Salt Agar mono plate, 90 x 15 mm CM9370P 10/pk
Mannitol Salt Slant CM9370S 10/pk
Mannitol Salt Broth CM9370B 10/pk

Quality Control

The following organisms are routinely used for testing for this medium.
Test OrganismsResults
Staphylococcus aureus (VRE) ATCC® 25923 Growth; yellow colonies and media
Staphylococcus epidermidis ATCC (VRE) ATCC® 12228 Growth; red colonies and media at 24-48 hours
Staphylococcus aureus (VRE) ATCC® 6538 Growth; yellow colonies and media at 18-24 hours
Proteus mirabilis (VRE) ATCC® 12453 Partial to complete inhibition
Escherichia coli (VRE) ATCC® 8739 Partial to complete inhibition

User Quality Control

Check for signs of contamination and deterioration. Users of commercially prepared media may be required to perform quality control testing with at least one known organism to demonstrate growth or a positive reaction; and at least one organism to demonstrate inhibition or a negative reaction (where applicable).

Ingredients g/L

(Final pH 7.4 +/- 0.2 at 25°C)
Sodium Chloride 75.0
Proteose Peptone 10.0
Mannitol 10.0
Beef Extract 1.0
Phenol Red 0.025
Agar 15.0
3 total citations

  1. American Public Health Association. 2004. Standard Methods for the Examination of Dairy Products, 17th ed. APHA, Washington, D.C.
  2. Vanderzant, C. and D.F. Splittstoesser, (ed.). 1992. Compendium of Methods for the Microbiological Examination of Foods,3rd ed. APHA, Washington, D.C.
  3. Chapman, G.H. 1945.J. Bacteriol.; 50:201.
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