- Mannitol salt agar (MSA) is a differential and selective media. It is selective because its high salt concentration (7.5 %) inhibits the growth of most bacteria. However, Staphylococcus is able to tolerate this high salinity.
- MSA is differential because it contains the sugar mannitol and phenol red, a pH indicator. When mannitol is fermented, acid products are produced and the pH drops. Phenol red is yellow in color below pH 6.8. Thus, mannitol fermenters such as Staphylococcus aureus will have a yellow halo around them. Mannitol nonfermenters such as Staphylococcus epidermidis will leave the MSA media unaltered (pink).
- Staphylococcus aureus causes such diseases as food poisoning, meningitis, osteomyelitis and toxic shock syndrome. Staphylococcus epidermidis is the predominant Staphylococcus species on the human skin. While usually considered to be part of the normal flora, it can act as an opportunistic pathogen in a compromised host.
Staphylococcus – Mannitol Salt Agar Plate
Manitol salt agar
