Which organism is isolated using 10B broth due to urease activity and alkaline pH?

• A. Mycoplasma genitalium
• B. Mycoplasma hominis
• C. Ureaplasma urealyticum
• D. Ureaplasma parvum

Answer: (C)

The test here hinges on urease activity and a pH change in a specialized medium. 10B broth provides urea as a substrate; organisms that produce urease hydrolyze the urea into ammonia, which raises the pH and shifts the indicator to alkaline. Only urease-positive organisms will produce that alkaline environment in this medium, making it useful for isolation.

Among the organisms listed, those that can hydrolyze urea and raise the pH are urease producers of the genus Ureaplasma. In particular, Ureaplasma urealyticum is a classic urease-positive species that will grow in 10B broth and cause the alkaline change, allowing its isolation by this method.

Mycoplasma genitalium and Mycoplasma hominis do not rely on urease for growth in this context. M. hominis metabolizes arginine instead (arginine dihydrolase pathway), so it would not produce the urease-driven pH shift in a urea-based medium. Ureaplasma parvum is also urease-positive, but the scenario described—isolation using 10B broth due to urease activity and alkaline pH—points to the well-characterized use of this medium with Ureaplasma urealyticum.