What color indicates a negative result in the malonate utilization test?

In the malonate utilization test, a negative result is indicated by the color green. This outcome occurs because, in the presence of malonate, bacteria that do not utilize this compound will not produce alkaline byproducts, preventing a shift in pH that would result in a color change. When there is no utilization, the pH indicator in the medium remains at its neutral state, which displays as green.

While a yellow color signifies a positive result due to the production of alkaline byproducts, the combination of green and yellow as options A and B might seem confusing. However, since yellow indicates positive utilization and green indicates negative utilization, it further affirms that green is indeed the color associated with a negative outcome in this particular test. Thus, the inclusion of both A and B effectively conveys that the primary focus is on the correct identification of the negative result.