Final answer:
Mannitol Salt Agar is a selective medium that differentiates Staphylococcus spp. based on mannitol fermentation, with S. aureus turning the agar yellow and non-fermenters like S. epidermidis leaving it red.
Step-by-step explanation:
The Mannitol Salt Agar (MSA) plate is a selective medium used to identify Staphylococcus spp. based on their physiological ability to tolerate high salt concentrations and ferment mannitol. The agar contains a high concentration of salt (7.5% NaCl), which inhibits most bacteria except for halotolerant species like staphylococci. The addition of mannitol and the pH indicator phenol red allows for the differentiation of species based on mannitol fermentation. When a species such as S. aureus ferments mannitol, the acidic byproducts cause the phenol red in the medium to turn yellow, indicating a positive test result. In contrast, species that do not ferment mannitol, like S. epidermidis, will grow without changing the color of the medium, resulting in a negative test for mannitol fermentation.
Mannitol Salt Agar (MSA) is a selective medium used to distinguish different species of Staphylococcus bacteria. It contains a high concentration of salt (7.5%), which inhibits the growth of bacteria susceptible to osmotic stress. The medium also contains mannitol, which is a fermentable substrate for some bacteria. When Staphylococcus aureus grows on MSA and ferments the mannitol, the medium changes from red to yellow due to the production of acids. Other species of Staphylococcus, such as Staphylococcus epidermidis, do not ferment mannitol, and the medium remains red.