Mac Conkey’s Agar is –
**Core Concept**
MacConkey's Agar is a selective and differential medium used for the isolation and identification of Gram-negative bacteria, particularly those that ferment lactose. It contains ingredients that inhibit the growth of Gram-positive bacteria and differential compounds that help differentiate lactose-fermenting and non-fermenting bacteria.
**Why the Correct Answer is Right**
MacConkey's Agar contains bile salts, which inhibit the growth of Gram-positive bacteria by disrupting their cell membranes. The agar also contains crystal violet, a dye that is reduced to a colorless form in the presence of Gram-positive bacteria, allowing them to be visualized. The differential compound lactose is used to differentiate lactose-fermenting bacteria, which produce acid and cause a change in pH, from non-fermenting bacteria, which do not produce acid.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to MacConkey's Agar.
**Option B:** Blood Agar is a different type of medium used for culturing bacteria and is not selective or differential like MacConkey's Agar.
**Option C:** Sabouraud's Agar is a medium used for culturing fungi and is not selective or differential like MacConkey's Agar.
**Clinical Pearl / High-Yield Fact**
Remember that MacConkey's Agar is used to differentiate lactose-fermenting and non-fermenting bacteria, which is a key step in identifying and isolating Gram-negative bacteria from clinical samples.
**Correct Answer:** A. MacConkey's Agar.