A yellow color in PRL and PRS indicates what type of byproduct?

The presence of a yellow color in PRL (Phenol Red Lactose) and PRS (Phenol Red Sucrose) indicates the production of acidic byproducts during fermentation. In microbiological media containing phenol red, which serves as a pH indicator, a color change occurs in response to the pH of the solution.

When microorganisms ferment carbohydrates present in the media (such as lactose or sucrose), they produce acids as metabolic byproducts. The accumulation of these acids lowers the pH of the medium, causing phenol red to change color from red (neutral pH) to yellow (acidic pH). This color shift is a clear visual indication that the organism is capable of fermenting the respective carbohydrate and generating acidic byproducts.

Thus, the yellow coloration signifies an environment with a lower pH due to the presence of these acids, confirming that the correct answer relates to acidic byproducts.