Koch, in 1942, reported that only staphylococci grow on agar media containing 7.5% sodium chloride (4).
Chapman further studied this phenomenon in greater detail and concluded that the addition of 7.5% sodium chloride to phenol red mannitol agar results in an improved medium for the isolation of plasma-coagulating staphylococci(5). Mannitol Salt Agar is listed as one of several media recommended for the enumeration of gram-positive bacteria incosmetics(6), clinical specimens(7-11), and pharmaceutical products(1).
The USP General Chapter <62> recommends Mannitol Salt Agar as a test medium for isolating Staphylococcus aureus in the Microbiological Examination of Nonsterile Products(1).
Mannitol Salt Agar is a nutritive medium due to its content of peptones and beef extract, which supply essential growth factors, such as nitrogen, carbon, sulfur and trace nutrients. The 7.5% concentration of sodium chloride results in the partial or complete inhibition of bacterial organisms other than staphylococci. Mannitol fermentation, as indicated by a change in the phenol red indicator, aids in the differentiation of staphylococcal species. Agar is a solidifying agent.
- United States Pharmacopeial Convention, Inc. 2008. The United States pharmacopeia 31/The national formulary 26, Supp. 1, 8-1-08, online. United States Pharmacopeial Convention, Inc., Rockville, Md.
- European Directorate for the Quality of Medicines and Healthcare. 2008. The European pharmacopoeia, 6th ed., Supp. 1, 4-1-08, online. European Directorate for the Quality of Medicines and Healthcare, Council of Europe, 226 Avenue de Colmar BP907-, F-67029 Strasbourg Cedex 1, France.
- Japanese Ministry of Health, Labour and Welfare. 2006. The Japanese pharmacopoeia, 15th ed., online. Japanese Ministry of Health, Labour and Welfare.
- Koch. 1942. Zentralbl. Bakteriol. Parasitenkd. Abt. I Orig. 149:122.
- Chapman. 1945. J. Bacteriol. 50:201.
- U. S. Food and Drug Administration. Bacteriological analytical manual, online. AOAC International, Gaithersburg, Md.
- Murray, Baron, Jorgensen, Landry and Pfaller (eds). 2007. Manual of clinical microbiology, 9th ed. American Society for Microbiology, Washington, D.C.
- Forbes, Sahm and Weissfeld. 2007. Bailey and Scott’s diagnostic microbiology, 12th ed. Mosby, Inc., St. Louis, Mo.
- MacFaddin. 2000. Biochemical tests for identification of medical bacteria, 3rd ed. Lippincott Williams & Wilkins, Baltimore, Md.
- Winn, Koneman, Allen, Janda, Procop, Schreckenberger and Woods (eds.). 2005. Koneman’s Color atlas and textbook of diagnostic microbiology, 6th Ed. Lippincott Williams & Wilkins, Baltimore, Md.
- Isenberg and Garcia (Ed). 2004 (update, 2007). Clinical microbiology procedures handbook, 2nd ed. American Society for Microbiology, Washington, D.C.