Mannitol salt agar or MSA is a selective and differential growth medium commonly used in microbiology. This encourages the growth of certain groups of bacteria while inhibiting the growth of others. This medium is important in medical laboratories by distinguishing pathogenic microbes in a short time. It contains high concentrations (about 7.5% -10%) of salt (NaCl), making it selective for Gram-positive bacteria ( Staphylococcus and Micrococcaceae) because this salt level is inhibiting for most other bacteria.. It is also a differential medium for mannitol-fermented staphylococci, containing carbohydrate mannitol and red phenol indicator, pH indicator for detecting acids produced by staphylococci mannitol-fermentation. Staphylococcus aureus produces yellow colonies with yellow zones, whereas other negative coagulase-negative staphylococcus produces small pink or red colonies with no discoloration of the medium. If an organism can ferment mannitol, an acidic by-product is formed which causes the red red phenol to become yellow. This is used for the selective isolation of predictive pathogen species (pp) Staphylococcus .
Video Mannitol salt agar
Expected results
- Gram Staphylococcus : fermentation of mannitol: the media turns yellow (e.g. S. aureus )
- Gram Staphylococcus : no fermentation of mannitol, being unchanged (eg S. epidermidis )
- Gram Streptococcus : growth stunted
- Gram -: growth stuck
Maps Mannitol salt agar
Typical composition
MSA usually contains:
- 5.0 g/L enzymatic digest of casein
- 5.0 g/L digest enzymatic animal tissue
- 1.0 g/L beef extract
- 10.0 g/L D-mannitol
- 75.0 g/L of sodium chloride
- 0.025 g/L phenol red
- 15.0 g/L order
- pH 7.4 Ã, Â ± 0.2 at 25Ã, Â ° C
References
External links
Source of the article : Wikipedia
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