10. Why does Staphylococcus aureus turn yellow on MSA?
A. the microbes have fermented lactose
B. the microbes are salt-tolerant
C. the microbes have fermented mannitol
D. the microbes are resistant to eosin and methylene blue
E. the microbes are resistant to phenol red
Staphylococcus aureus turns mannitol salt agar (MSA) into yellow. Because it ferments mannitol and produces acid as a byproduct which changes the color of the indicator phenol red into yellow.