MANNITOL SALT AGAR TEST

Objective:

To determine the ability of an organism to grow in 7.5% NaCl and ferment mannitol.

Test Procedure

1. Streak an MSA plate with a light line of inoculum from the pure culture of the test organism using a sterile loop.
2. Incubate at 30°C for at least 48 hours.

Interpretation

Any significant growth indicates the organism is a Staphylococcus species. The phenol red indicator changes to yellow at low (acid) pH, which is a product of fermentation. Therefore, fermentation of mannitol will change the color of agar to yellow. Orange is negative.

• Positive: Growth, yellow color (mannitol "+").
• Negative: Growth or no growth; red or orange color (mannitol "−").