Mannitol Salt Agar (MSA) Plate Test:

If given description of results, know what that means about the organism’s ability to live on salt, and possibly its ability to ferment mannitol

• SELECTIVE! Salt (NaCl) in media inhibits the growth of organisms that cannot grow on salt 

• DIFFERENTIAL! Phenol Red pH indicator will change color of media if organism can ferment (produce acid) the sugar Mannitol

If given the details of an organism's ability to live on salt and/or ferment mannitol, be able to describe how the results should come out (growth and/or changes in the color of the media 

• Positive mannitol: yellow agar the organism is salt tolerant and ferment mannitol 

• Negative mannitol: red/pink agar the organism is salt talent but does not ferment mannitol 

• No growth: not salt tolerant

You inoculate a Mannitol Salt Agar (MSA) plate with an unknown organism. After incubation you observe growth on the plate and the color of the plate surrounding the growth is pink. What TWO things does this tell you about the unknown organism 

Negative does not have the ability to ferment Mannitol 

You inoculate an unknown organism on a Mannitol Salt Afar (MSA) plate. After incubation, you observe that there is no growth. What does this tell you about the organism?

It cannot live on NaCl 

You inoculate a Mannitol Salt Agar (MSA) plate with an unknown organism. After incubation you observe growth on the plate and the color of the plate surrounding the growth is yellow. What TWO things does this tell you about the unknown organism 

Positive it can ferment mannitol and survive on NaCl