How do mannitol-salt agar tests work?

Answer 1

Mannitol salt agar supports growth of organisms that can grow in a high salt concentration, particularly Staphylococcus species and halophiles. The phenol red pH indicator in the agar will also let you know whether or not the bacterium you streaked ferments mannitol by changing to a yellow color if fermentation has occured.

Answer 2

Mannitol-salt agar contains a high concentration of salt, and thus is selective for halophiles--organisms that prefer salty environments. A common example of this would be organisms in the genus Staphylococcus, which are found on human skin.

It is differential based on an organisms' ability to metabolize mannitol, a sugar. Organisms that metabolize mannitol and have acidic byproducts will turn the medium yellow, as it contains phenol red, a pH indicator.

Answer 3

Staphylococcus can grow well on mannitol salt agar because it can tolerate high saline. It prefers to grown on a salty or saline medium in order to grow at all.