Question

1. msa is selective due to its high concentration of: a. bile salts b. crystal violet c. nacl (salt) d. phenol red 10. a yellow zone on msa indicates: a. protein digestion b. mannitol fermentation c. glucose breakdown d. capsule presence 11. in phenol red broth, a yellow color indicates: a. alkaline byproducts b. acid production from fermentation c. protein degradation d. no growth

Explanation:

• MSA (Mannitol Salt Agar) is selective due to its high - concentration of NaCl which inhibits the growth of most non - halotolerant bacteria.
• A yellow zone on MSA indicates mannitol fermentation as the fermentation of mannitol produces acids which change the color of the pH indicator (phenol red) to yellow.
• In phenol red broth, a yellow color indicates acid production from fermentation as phenol red turns yellow in acidic conditions.

Answer:

1. C. NaCl (salt)
2. B. Mannitol fermentation
3. B. Acid production from fermentation