Final answer:
MacConkey agar is the best agar for testing urine for E. coli. E. coli colonies on MacConkey agar appear as bright pink.
Step-by-step explanation:
The best agar for testing urine for E. coli is MacConkey agar. On this agar, E. coli colonies appear as bright pink. The agar contains lactose, which E. coli can ferment, resulting in the production of acid and the dissolution of the neutral red indicator. This causes the colonies to turn pink. Other non-lactose fermenters would appear either colorless or a different color, such as cream-colored streaks.