Mannitol Salt Agar – Selective & Differential Microbiology Medium

Mannitol Salt Agar (MSA) is a selective and differential microbiological culture medium commonly used for the isolation and differentiation of staphylococci. Its high sodium chloride concentration provides selective action by inhibiting many other bacteria, while mannitol and the phenol-red indicator enable differentiation based on mannitol fermentation. Typical formulations contain approximately 7.5% sodium chloride, mannitol, peptones or nutrient extracts, phenol red and agar. Organisms capable of fermenting mannitol produce acid, causing the phenol-red indicator to change from red toward yellow around growth.