Like this study set? Create a free account to save it.

Sign up for an account

Already have a Quizlet account? .

Create an account


3 Broth Cultures

Escherichia Coli
Staphylococcus Epidermidis
Staphylococcus Aureus

Mannitol salt is both:

Selective media & Differential media

Selective Media

Favors growth of Staphylococcus species
Inhibits growth of Gram (-) bacteria

Differential Media

Isolate Staphylococcus aureus from other staph species

MSA Contains:

1.NaCl-7.5%-inhibits Gram (-) bacteria (E. Coli)

S. aurerus produces enzyme-mannitol dehydrogenase-breaks mannitol into pyruvate which ferments to produce an acid

3. Phenol Red-pH indicator
Yellow (acid) < 6.8
Red (neutral) 7.4-8.4
Pink (base) > 8.4

1. What purpose does the Nutrient Agar plate serve? In what way does it increase validity of the test result?

Serves as a control
Increases validity-shows that Gram (-) bacteria (e. coli) are viable

What would be the likely consequence of omitting the NaCl in Mannitol Salt Agar? Why?

Salt is the selective ingredient. With no NaCl, all organisms, Gram (+) & Gram (-) would grow equally

With the diversity of microorganisms in the world, how can a single test such as MSA be used to confidently identify staphylococcus aures?

Salt levels in MSA inhibit all Gram (-) leaving gram (+) cells.
Only staph species can tolerate high salt, eliminating all other gram (+) microbes

Only S. Aures can ferminent mannitol, eliminating all other staph species.


E. Coli-no growth! Why? 7.5% salt inhibition

S. Aureus-Yellow!-Enzyme breakdown Mannitol-produce acid

S. Epidermidis

S. Aures fermits mannitol acid (yellow)
S. Epidermidis grows but cant fermit mannitol-no acid
E. Coli-No growth-high salt

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions and try again


Reload the page to try again!


Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

Voice Recording