Embedded Files
General Information About the Mannitol Salt Agar Test
General Information About the Mannitol Salt Agar Test
Mannitol Salt Agar (MSA) is a selective and differential medium. The high concentration of salt (7.5%) selects for members of the genus Staphylococcus since they can tolerate high saline levels. Organisms from other genera may grow, but they typically grow very weakly.
The Basic Chemistry of Mannitol Salt Agar
The Basic Chemistry of Mannitol Salt Agar
In addition to the 7.5% NaCl, MSA also contains the sugar mannitol and the pH indicator phenol red. If an organism can ferment mannitol, an acidic byproduct is formed that will cause the phenol red in the agar to turn yellow.
Reading the Results
Reading the Results
Most pathogenic staphylococci, such as Staphylococcus aureus, will ferment mannitol. Most non-pathogenic staphylococci, such as Staphylococcus epidermidis will not ferment mannitol.
The Staphylococcus aureus</i> on the left ferments the mannitol, turning the agar yellow. The Staphylococcus epidermidis on the right does not ferment mannitol, and the medium stays red.
Application of the Mannitol Salt Agar Test
Application of the Mannitol Salt Agar Test
You may elect to use the Mannitol Salt Agar test to differentiate between Staphylococcus aureus and Staphylococcus epidermidis when performing your Gram positive unknown. Another option is to perform the coagulase test.
Page updated
Report abuse