Which of the following terms correctly apply to MacConkey agar?

• A. Complex and transport
• B. Enriched and reducing
• C. Synthetic and supportive
• D. Selective and differential

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the purpose of MacConkey agar. It is designed to isolate and differentiate gram-negative bacteria, especially members of the Enterobacteriaceae family.
2. Step 2: Recall that selective media contain components that inhibit the growth of certain groups of microorganisms while allowing others to grow. MacConkey agar contains bile salts and crystal violet, which inhibit gram-positive bacteria, making it selective for gram-negative bacteria.
3. Step 3: Recognize that differential media contain indicators that allow differentiation between organisms based on their biological characteristics. MacConkey agar contains lactose and a pH indicator (neutral red) to differentiate lactose fermenters (which produce acid and turn the medium pink) from non-fermenters (which do not change the color).
4. Step 4: Compare the given options with the characteristics of MacConkey agar: it is not complex and transport, nor enriched and reducing, nor synthetic and supportive. Instead, it is selective (due to inhibitors) and differential (due to lactose and pH indicator).
5. Step 5: Conclude that the correct terms describing MacConkey agar are 'selective and differential' because it selectively allows growth of gram-negative bacteria and differentiates them based on lactose fermentation.