Prepared Plated Media PPM

MANNITOL SALT AGAR

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Catalog Number : 917

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Description

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MANNITOL SALT AGAR (MSA) is a selective medium prepared according to the recommendations of Chapman for the isolation of presumptive pathogenic staphylococci. Most of the other bacteria are inhibited by the high concentration of Sodium chloride.The Peptone mixture and Beef extract provide nitrogen, vitamins, minerals and amino acids essential for growth. Mannitol is the carbohydrate energy source and Phenol red is the pH indicator. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Bacteriological agar is the solidifying agent.The degradation of mannitol by bacteria produces acidic products that change the color of the medium from pink to yellow. Due to its high content of sodium chloride, a heavy inoculum of the material in study can be used.The European Pharmacopeia recommends in the Paragraph 2.6.13 “Microbiological examination of non-sterile products: Test for specifi ed microorganisms”. After incubation in Casein Soya Bean Digest Broth (TSB Cat. 1224) at 30 - 35°C for 18 - 24 hours, subculture on a plate of Mannitol Salt Agar (MSA), the incubation of the plates at 30 - 35°C for 18 - 72 hours for growing promotion test and also to inoculate and incubate Escherichia coli ATCC 8739 as negative control. The mannitol fermenting pathogenic staphylococci are large and are surrounded by a yellow zone, colonies of non-pathogenic staphylococci appear as small colonies surrounded by a red or purple zone.Interpretation: The possible presence of S. aureus is indicated by the growth of yellow /white colonies surrounded by a yellow zone. This is confi rmed by identifi cation test.The product complies with the test if colonies of the types described are not present or if the confi rmatory identifi cation tests are negative.The addition of 5% Egg Yolk Emulsion (Cat. 5152) allows to detect the lipase activity of staphylococci, as well as mannitol fermentation. The high concentration of salt in the medium clears the egg yolk emulsion, and lipase production is detected as a yellow opaque zone around the colonies of staphylococci producing this enzyme. This phenomenon, together with a positive coagulase test, confi rms the organism as a pathogenic Staphylococcus.Inoculate and incubate at 35 ± 2°C and observe after 18 - 24 hours and after 48 hours.