Which selective agar is commonly used for isolating Enterobacteriaceae from clinical specimens?

Which selective agar is commonly used for isolating Enterobacteriaceae from clinical specimens?

• A. MacConkey agar
• B. XLD (Xylose-Lysine-Deoxycholate) agar
• C. MEA (Malt Extract Agar)
• D. Sabouraud agar

Answer: (B)

The correct answer indicates that XLD (Xylose-Lysine-Deoxycholate) agar is commonly used for isolating Enterobacteriaceae from clinical specimens. This selective medium is particularly effective due to its ability to differentiate organisms based on their fermentation capabilities. XLD agar contains xylose, lysine, phenol red indicator, and sodium thiosulfate, allowing for the identification of specific groups within the Enterobacteriaceae family. For instance, those organisms that can ferment xylose will produce acids, lowering the pH and changing the color of the medium, which aids in isolating and identifying Enterobacteriaceae like Salmonella and Shigella based on their metabolic properties. The other options—MacConkey agar, MEA, and Sabouraud agar—serve different purposes. While MacConkey agar is also a selective medium for gram-negative bacteria, and it selective for lactose fermenters, it does not differentiate as effectively as XLD for specific Enterobacteriaceae. MEA is primarily used for fungi, while Sabouraud agar is designed to cultivate yeasts and molds, making them unsuitable for isolating Enterobacteriaceae. Overall, XLD has been specifically tailored to provide both selective isolation and

The correct answer indicates that XLD (Xylose-Lysine-Deoxycholate) agar is commonly used for isolating Enterobacteriaceae from clinical specimens. This selective medium is particularly effective due to its ability to differentiate organisms based on their fermentation capabilities.

XLD agar contains xylose, lysine, phenol red indicator, and sodium thiosulfate, allowing for the identification of specific groups within the Enterobacteriaceae family. For instance, those organisms that can ferment xylose will produce acids, lowering the pH and changing the color of the medium, which aids in isolating and identifying Enterobacteriaceae like Salmonella and Shigella based on their metabolic properties.

The other options—MacConkey agar, MEA, and Sabouraud agar—serve different purposes. While MacConkey agar is also a selective medium for gram-negative bacteria, and it selective for lactose fermenters, it does not differentiate as effectively as XLD for specific Enterobacteriaceae. MEA is primarily used for fungi, while Sabouraud agar is designed to cultivate yeasts and molds, making them unsuitable for isolating Enterobacteriaceae.

Overall, XLD has been specifically tailored to provide both selective isolation and