Biochemical identification – urease activity: Which organism(s) classically show a positive urease test when grown under standard laboratory conditions?

Introduction / Context:
The urease test detects the enzyme urease, which hydrolyzes urea to ammonia and carbon dioxide. Ammonia raises pH, changing phenol red indicator from yellow to pink, aiding rapid screening of certain Enterobacterales and other taxa.

Given Data / Assumptions:

• Proteus spp. are strongly urease positive (rapid splitters).
• Klebsiella spp. are typically urease positive (often slower than Proteus).
• E. coli is classically urease negative.

Concept / Approach:
Strong urease activity is a hallmark of Proteus, explaining clinical associations such as struvite stone formation. Klebsiella also produces urease and can alkalinize media, though kinetics may vary. Thus, both genera are expected to yield positive tests under routine conditions.

Step-by-Step Solution:
Evaluate each listed genus for urease production. Recognize Proteus and Klebsiella as positive; exclude E. coli. Choose the combined option (both a and b).

Verification / Alternative check:
QC strains like Proteus vulgaris (positive) and E. coli (negative) confirm media and reagent integrity.

Why Other Options Are Wrong:
Selecting only one omits another true positive. “None” is incompatible with established biochemical profiles; E. coli is a known negative control.

Common Pitfalls:
Reading the reaction too early for slow urease producers; misinterpreting weak color shifts without controls.

Final Answer:
Both (a) and (b).