Mannitol Salt Agar Culture Medium

Mannitol Salt Agar (MSA), also called Chapman Agar, is a selective and differential medium used in microbiology to isolate and identify staphylococci, especially Staphylococcus aureus.

Key Characteristics:

Selectivity:

• Contains 7.5% sodium chloride, creating a high-salt environment that inhibits most bacteria except halotolerant staphylococci.

Differentiation:

• Distinguishes staphylococcal species based on mannitol fermentation:

  • Mannitol Fermenters (e.g., S. aureus): Produce acid, turning the phenol red pH indicator from red to yellow around colonies.

  • Non-Fermenters (e.g., S. epidermidis): No acid production; the medium stays red or may turn magenta.

Nutrient Composition:

• Includes peptones and beef extract to support bacterial growth.

Applications:

• Used for isolating pathogenic staphylococci from clinical, food, cosmetic, and water samples.