In a genital culture using 10B broth, an alkaline reaction without turbidity indicates which organism?

In a genital culture using 10B broth, an alkaline reaction without turbidity indicates which organism?

• A. Mycoplasma genitalium
• B. Mycoplasma hominis
• C. Ureaplasma urealyticum
• D. pH change due to molecules in the clinical specimen

Answer: (C)

In this setup, the medium contains urea and a pH indicator. If an organism has urease, it splits urea into ammonia and carbon dioxide, raising the pH and producing an alkaline change in the medium. Ureaplasma urealyticum is urease-positive, so it can alkalinize the broth even when there’s no visible growth (turbidity). That combination—alkaline pH without turbidity—points to Ureaplasma urealyticum. Mycoplasma genitalium does not produce urease on this substrate, and Mycoplasma hominis relies on arginine metabolism rather than urease, so they wouldn’t explain the same alkaline shift in a urea-containing 10B broth. The option about pH change due to molecules in the clinical specimen isn’t tied to a specific organism.

In this setup, the medium contains urea and a pH indicator. If an organism has urease, it splits urea into ammonia and carbon dioxide, raising the pH and producing an alkaline change in the medium. Ureaplasma urealyticum is urease-positive, so it can alkalinize the broth even when there’s no visible growth (turbidity). That combination—alkaline pH without turbidity—points to Ureaplasma urealyticum. Mycoplasma genitalium does not produce urease on this substrate, and Mycoplasma hominis relies on arginine metabolism rather than urease, so they wouldn’t explain the same alkaline shift in a urea-containing 10B broth. The option about pH change due to molecules in the clinical specimen isn’t tied to a specific organism.