pH of sabourauds dextrose agar is adjusted to?
**Core Concept**
The pH of Sabouraud's Dextrose Agar (SDA) is adjusted to create an environment that selectively promotes the growth of fungi, particularly dermatophytes and yeasts. This is crucial for isolating and identifying fungi from clinical specimens.
**Why the Correct Answer is Right**
The pH of SDA is adjusted to 5.6, which is slightly acidic. This acidic environment inhibits the growth of most bacteria, while allowing fungi to thrive. The presence of dextrose (glucose) in the agar serves as a carbon source for the fungi, promoting their growth.
**Why Each Wrong Option is Incorrect**
**Option A:** pH 7.4 - This is the normal pH of human blood, which would not selectively inhibit bacterial growth and favor fungal growth.
**Option B:** pH 4.5 - While acidic, this pH is too low for optimal growth of many fungi, particularly dermatophytes.
**Option C:** pH 6.8 - This pH is closer to neutral and would not effectively inhibit bacterial growth, allowing contaminants to overgrow the desired fungal isolates.
**Clinical Pearl / High-Yield Fact**
When culturing fungal pathogens, the pH of the growth medium is a critical factor in selecting the optimal conditions for their growth. A pH of 5.6 in Sabouraud's Dextrose Agar is a standard condition that allows for the isolation and identification of various fungal species.
**Correct Answer:** C. pH 5.6