Question

Consider a culture medium on which only gram-positive organisms such as Staphylococcus aureus colonies can grow due to an elevated NaCl level. A yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the pH as a result and changing the color of a pH indicator chemical. This type of medium would be referred to as a(n) __________.

Answer 1

This type of medium would be referred as a selective and differential medium.

Step-by-step explanation:

In a differential medium species that do and do not carry out a biochemical process can be distinguished from each other with the help of certain chemicals. Visual proof helps the distinguishing process.

Here the bacterial colony ferments the sugar in the medium and decreases the pH of the medium. This pH change is indicated by the yellow halo formed around the bacterial colony and is a visual proof to the biochemical process that just took place in the medium.

When a mixed culture is a selective media it contains certain ingredients that inhibit the growth of one species of microbes and promotes the growth of other. The medium containing elevated levels of NaCl becomes a selective medium promoting the growth of staphylococcus aureus.