Mannitol Salt Agar (MSA) Plate






I. Staphylococcus epidermidis (Gram positive) - growth but no yellow halo

II. Escherichia coli (Gram negative) - No growth

III. Staphylococcus aureus (Gram positive) - growth with yellow halo

IV. Psuedomonas aeruginosa (Gram negative) - no growth

Mannitol Salt Agar (MSA) is used to determine if the bacteria is halophilic (salt loving) and if the bacteria can ferment mannitol.  If the bacteria is able to grow then it is a halophilic bacteria, due to it's ability to grow in a high salt environment.  A positive result for mannitol fermentation would be the formation of a yellow halo around the bacterial colony, this is an indication of acid production from the breakdown of mannitol.