Mannitol Salt Agar 1) Remove the culture from the incubator and observe the grow

Question

Mannitol Salt Agar

1) Remove the culture from the incubator and observe the growth. Provide results for these two tests (Circle or highlight):

Growth on 7.5% NaCl:        +      -

Mannitol Fermentation:      +      -

2) What result would be expected in the “growth in 6.5% NaCl test” for bacteria capable of growth on mannitol salt agar? Explain.

3) Find the recipe for mannitol salt agar. List each of the components in the space below. For each component, explain whether it is differential, selective, both differential and selective, or none (meaning it does not distinguish between any bacterial types).

Explanation / Answer

1. Mannitol salt agar medium contains high concentrations of salt (approximately 7.5% to 10%) and mannitol as a source of carbon. Only gram positive staphylococcus bacteria can grow in this media, while the growth of gram negative and other microorganisms is inhibited. For example, staphylococcus aureus can ferment mannitol and grow in high salt conditions, the resulting bacterial growth produces yellow colonies.

2. Positive test result would be expected in the “growth in 6.5% NaCl test” for bacteria capable of growth on mannitol salt agar media because they can grow in high salt concentrations.

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