Question:
Which of the following selective media may be utilized for the detection of Salmonella
A. Xylose Lysine Deoxycholate Agar
B. Hektoen Enteric Agar
C. MacConkey agar
D. Wilson and Blair Bismuth Sulphite Agar
Choose the correct answer from the options given below:
Which of the following selective media may be utilized for the detection of Salmonella
A. Xylose Lysine Deoxycholate Agar
B. Hektoen Enteric Agar
C. MacConkey agar
D. Wilson and Blair Bismuth Sulphite Agar
Choose the correct answer from the options given below:
A. Xylose Lysine Deoxycholate Agar
B. Hektoen Enteric Agar
C. MacConkey agar
D. Wilson and Blair Bismuth Sulphite Agar
Choose the correct answer from the options given below:
Show Hint
Specific selective media for Salmonella contain indicators for hydrogen sulfide ($H_2S$) production (like iron salts), which yields characteristic black-centered colonies on HE, XLD, and Bismuth Sulphite Agar.
Updated On: Aug 13, 2026
- B only
- A, B and D only
- A and C only
- A, C and D only
Show Solution
Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Culturing fastidious or enteric pathogens from clinical or environmental samples containing mixed flora requires selective and differential media.
Selective media contain inhibitory agents (like bile salts, dyes, or heavy metals) that suppress unwanted background organisms while allowing the target pathogen to grow.
Detailed Explanation:
Let us review the listed media for isolating Salmonella:
- A. Xylose Lysine Deoxycholate (XLD) Agar: A selective and differential medium. Sodium deoxycholate inhibits Gram-positive bacteria. It differentiates based on xylose fermentation, lysine decarboxylation, and hydrogen sulfide ($H_2S$) production. Salmonella forms red colonies with black centers.
- B. Hektoen Enteric (HE) Agar: Designed to isolate and differentiate Salmonella and Shigella from other enterics. Bile salts inhibit Gram-positive organisms. Fermentation indicators and ferric ammonium citrate detect $H_2S$, showing Salmonella as blue-green colonies with black centers.
- C. MacConkey Agar: A general-purpose selective and differential medium for Gram-negative enteric bacilli, but not highly selective for Salmonella because it permits the growth of all coliforms. It is not considered a specific selective medium for Salmonella detection.
- D. Wilson and Blair Bismuth Sulphite Agar: A highly selective medium specifically designed for isolating Salmonella (especially Salmonella enterica serovar Typhi) from clinical specimens. Bismuth sulfite and brilliant green inhibit coliforms while allowing Salmonella to grow, forming flat, black colonies with a metallic sheen.
Therefore, the highly selective media utilized specifically for the isolation and detection of Salmonella are XLD, HE, and Bismuth Sulphite Agar.
Step 2: Final Answer:
The correct combination is A, B and D only, which is Option (B).
Culturing fastidious or enteric pathogens from clinical or environmental samples containing mixed flora requires selective and differential media.
Selective media contain inhibitory agents (like bile salts, dyes, or heavy metals) that suppress unwanted background organisms while allowing the target pathogen to grow.
Detailed Explanation:
Let us review the listed media for isolating Salmonella:
- A. Xylose Lysine Deoxycholate (XLD) Agar: A selective and differential medium. Sodium deoxycholate inhibits Gram-positive bacteria. It differentiates based on xylose fermentation, lysine decarboxylation, and hydrogen sulfide ($H_2S$) production. Salmonella forms red colonies with black centers.
- B. Hektoen Enteric (HE) Agar: Designed to isolate and differentiate Salmonella and Shigella from other enterics. Bile salts inhibit Gram-positive organisms. Fermentation indicators and ferric ammonium citrate detect $H_2S$, showing Salmonella as blue-green colonies with black centers.
- C. MacConkey Agar: A general-purpose selective and differential medium for Gram-negative enteric bacilli, but not highly selective for Salmonella because it permits the growth of all coliforms. It is not considered a specific selective medium for Salmonella detection.
- D. Wilson and Blair Bismuth Sulphite Agar: A highly selective medium specifically designed for isolating Salmonella (especially Salmonella enterica serovar Typhi) from clinical specimens. Bismuth sulfite and brilliant green inhibit coliforms while allowing Salmonella to grow, forming flat, black colonies with a metallic sheen.
Therefore, the highly selective media utilized specifically for the isolation and detection of Salmonella are XLD, HE, and Bismuth Sulphite Agar.
Step 2: Final Answer:
The correct combination is A, B and D only, which is Option (B).
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