What is the result of a positive urease test for Enterobacteriaceae?

• A. The medium turns yellow due to acid production.
• B. The medium remains unchanged.
• C. The medium turns pink due to the production of ammonia.
• D. The medium turns green due to gas production.

Answer: (C)

A positive urease test for Enterobacteriaceae indicates that the organism can hydrolyze urea into ammonia and carbon dioxide. This biochemical reaction raises the pH of the medium because ammonia is alkaline, leading to a color change in the indicator often used in urease tests, typically phenol red.

When urea is broken down by urease activity, the medium becomes more alkaline, resulting in a pink coloration. This color change confirms the presence of urease, as the phenol red indicator responds to the shift in pH. Therefore, the result of a positive urease test is the medium turning pink due to the production of ammonia from urea hydrolysis.

Other potential results do not accurately reflect the nature of the urease test. For example, a yellow medium would suggest acid production rather than alkaline ammonia production, while an unchanged medium would indicate a negative urease result. Similarly, gas production does not lead to a green coloration in this context, reaffirming that the correct answer reflects the actual biochemical process involved in urease activity.