Mannitol salt agar - Wikipedia Mannitol salt agar An MSA plate with Micrococcus sp. ( 1 ), Staphylococcus epidermidis ( 2 ) and S. aureus colonies ( 3 ). Mannitol salt agar or MSA is a commonly used selective and differential growth medium in microbiology. It encourages the growth of a group of certain bacteria while inhibiting the growth of others. This medium is important in medical laboratories by distinguishing pathogenic microbes in a short period of time. It contains a high concentration ( about 7.5 % - 10 % ) of salt ( NaCl ), making it selective for Gram - positive bacteria ( Staphylococcus and Micrococcaceae ) since this level of salt is inhibitory to most other bacteria. It is also a differential medium for mannitol - fermenting staphylococci, containing carbohydrate mannitol and the indicator phenol red, a pH indicator for detecting acid produced by mannitol - fermenting staphylococci. Staphylococcus aureus produces yellow colonies with yellow zones, whereas other coagulase - negative staphylococci produce small pink or red colonies with no colour change to the medium. If an organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red in the agar to turn yellow. It is used for the selective isolation of presumptive pathogenic ( pp ) Staphylococcus species. Colonies of Staphylococcus on Chapman 's media Contents 1 Expected results 2 Typical composition 3 References 4 External links Expected results Gram + Staphylococcus : fermenting mannitol : medium turns yellow ( e.g. S. aureus ) Gram + Staphylococcus : not fermenting mannitol, medium does not change color ( e.g. S. epidermidis ) Gram + Streptococcus : inhibited growth Gram - : inhibited growth Typical composition MSA typically contains : 5.0 g / L enzymatic digest of casein 5.0 g / L enzymatic digest of animal tissue 1.0 g / L beef extract 10.0 g / L D - mannitol 75.0 g / L sodium chloride 0.025 g / L phenol red 15.0 g / L agar pH 7.4 ± 0.2 at 25 ° C References ^ Jump up to : Bachoon, Dave S. ; Dustman, Wendy A. ( 2008 ). `` Exercise 8 : Selective and Differential Media for Isolation ''. In Michael Stranz. Microbiology Laboratory Manual. Mason, OH : Cengage Learning. Jump up ^ `` Mannitol salt agar '' ( PDF ). Becton, Dickinson and Company. 2005. Jump up ^ Anderson, Cindy ( 2013 ). Great Adventures in the Microbiology Laboratory. Pearson. pp. 175 -- 176. ISBN 978 - 1 - 269 - 39068 - 2. Jump up ^ `` Mannitol salt agar ( 7143 ) '' ( PDF ). Neogen Corp. 2008. Jump up ^ Identification of Staphylococcus aureus : DNase and Mannitol salt agar improve the efficiency of the tube coagulase test Jump up ^ The United States Pharmacopeia ( 23rd ed. ). Rockville, MD : The United States Pharmacopeial Convention. 1995. External links Growth media / agar plates Selective media Gram positive Actinobacteria Mycobacterium tuberculosis Löwenstein -- Jensen medium Middlebrook 7H9 Broth Middlebrook 7H10 Agar Middlebrook 7H11 Agar Mycoplasma pneumoniae Eaton 's agar Firmicutes Corynebacterium diphtheriae Hoyle 's agar Enterococcus Bile esculin agar Lactobacillus MRS agar Lactococcus M17 agar Staphylococcus Mannitol salt agar Gram negative Alphaproteobacteria Brucella Brucella agar Farrell 's medium Betaproteobacteria Neisseria Thayer - Martin agar Gammaproteobacteria Bordetella Bordet - Gengou agar Enterobacteriaceae VRBD agar Haemophilus influenzae / Legionella pneumophila Buffered charcoal yeast extract agar Pseudomonas aeruginosa Cetrimide agar Salmonella XLT agar DCA agar Salmonella / Shigella XLD agar Differential media Lactose fermenting gram negative MacConkey agar / Sorbitol - MacConkey agar Eosin methylene blue Hektoen enteric agar sulfur Bismuth sulfite agar Fungal media Czapek medium Dermatophyte test medium Potato dextrose agar Sabouraud agar Nonselective media Chocolate agar Nutrient agar Plate count agar Other / ungrouped media Cystine lactose electrolyte deficient agar Cystine tryptic agar Endo agar Lysine iron agar slant Müller - Hinton agar / PNP agar R2a agar Simmons ' citrate agar Trypticase soy agar Tryptic soy broth TSI slant This microbiology - related article is a stub. You can help Wikipedia by expanding it. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Mannitol_salt_agar&oldid=807212136 '' Categories : Microbiological media Microbiology stubs Talk Contents About Wikipedia Català Deutsch Español Français Italiano മലയാളം 日本 語 Polski ไทย 中文 4 more Edit links This page was last edited on 26 October 2017, at 16 : 33. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: what is the role of phenol red in the mannitol salt medium
Answer: a pH indicator for detecting acid