Question:
The medium used for detecting Staphylococci in dairy products
The medium used for detecting Staphylococci in dairy products
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To identify staphylococci on Baird-Parker agar:
Look for black, shiny, convex colonies surrounded by a clear zone (halo) within 48 hours of incubation.
The black color is due to tellurite reduction, and the halo is due to lecithinase activity.
Look for black, shiny, convex colonies surrounded by a clear zone (halo) within 48 hours of incubation.
The black color is due to tellurite reduction, and the halo is due to lecithinase activity.
Updated On: Jul 23, 2026
- MacConkey agar
- McClung Toabe agar
- Malt Extract agar
- Baird Parker agar
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Selective and differential media are used to isolate and enumerate specific bacterial pathogens from dairy products while suppressing background competitive flora.
Each medium uses specific inhibitors and diagnostic indicators to identify target species.
Step 2: Detailed Explanation:
Let us analyze the applications of the media listed in the options:
- (A) MacConkey Agar:
This is a selective and differential medium used to detect coliforms and other Gram-negative enteric bacteria.
It contains bile salts and crystal violet to inhibit Gram-positive organisms.
- (B) McClung Toabe Agar:
This medium is used to detect lecithinase activity in anaerobic sporeformers, such as Clostridium species.
- (C) Malt Extract Agar:
This is an acidic medium used to isolate and enumerate yeasts and molds in dairy products.
- (D) Baird-Parker Agar:
This is the standard selective and differential medium used to detect and enumerate Staphylococcus aureus in foods.
- It contains lithium chloride and potassium tellurite, which act as selective agents to inhibit most other Gram-positive and Gram-negative bacteria.
- It contains egg yolk emulsion as a differential diagnostic agent.
- Coagulate-positive S. aureus reduces tellurite, forming shiny, jet-black colonies.
- It also hydrolyzes egg yolk lecithin, forming a distinct clear zone (halo) around the black colonies.
Step 3: Final Answer:
The standard medium used for detecting Staphylococci in dairy products is Baird-Parker agar.
Selective and differential media are used to isolate and enumerate specific bacterial pathogens from dairy products while suppressing background competitive flora.
Each medium uses specific inhibitors and diagnostic indicators to identify target species.
Step 2: Detailed Explanation:
Let us analyze the applications of the media listed in the options:
- (A) MacConkey Agar:
This is a selective and differential medium used to detect coliforms and other Gram-negative enteric bacteria.
It contains bile salts and crystal violet to inhibit Gram-positive organisms.
- (B) McClung Toabe Agar:
This medium is used to detect lecithinase activity in anaerobic sporeformers, such as Clostridium species.
- (C) Malt Extract Agar:
This is an acidic medium used to isolate and enumerate yeasts and molds in dairy products.
- (D) Baird-Parker Agar:
This is the standard selective and differential medium used to detect and enumerate Staphylococcus aureus in foods.
- It contains lithium chloride and potassium tellurite, which act as selective agents to inhibit most other Gram-positive and Gram-negative bacteria.
- It contains egg yolk emulsion as a differential diagnostic agent.
- Coagulate-positive S. aureus reduces tellurite, forming shiny, jet-black colonies.
- It also hydrolyzes egg yolk lecithin, forming a distinct clear zone (halo) around the black colonies.
Step 3: Final Answer:
The standard medium used for detecting Staphylococci in dairy products is Baird-Parker agar.
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