A physician orders a urea breath test; she must suspect an infection caused by which organism?

• A. Citrobacter freundii
• B. Campylobacter jejuni
• C. Providencia rettgeri
• D. Helicobacter pylori

Answer: (D)

The main idea is that the urea breath test detects urease activity in the stomach, which is a hallmark of Helicobacter pylori infection. When a patient drinks urea labeled with carbon, H. pylori’s urease enzyme rapidly splits it into ammonia and CO2. If the labeled CO2 is detected in the breath, it indicates the presence of the urease-producing organism in the stomach. Among the organisms listed, Helicobacter pylori is the one known to colonize the stomach and produce urease, enabling the test to work. The other organisms listed do not typically reside in the stomach in a urease-active form that would yield a positive urea breath test, so they are not diagnosed by this test.