Phenol Red (PR) Broth is a differential test medium prepared as a base to which a carbohydrates is added. Included in the base medium are peptone and the pH indicator phenol red. We will inoculate PR Glucose Broths with three organisms to determine their fermentation characteristics.

Q1. Suppose you innoculate a PR broth with a slow-growing fermenter. After 48 hours, you see slight turbidity but score it as (-/-). Is this result a false positive or a false negative? Is this a result of poor specificity or poor sensitivity of the test system?

Q2. Early formulations of this medium used a smaller amount of carbohydrate and occasionally produced false alkaline (pink) results after 48 hours. Why do you think this happened? List at least two steps, as a microbiologist, that you could take to prevent the problem.