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Questions and Answers
What is the primary purpose of using MacConkey agar?
What is the primary purpose of using MacConkey agar?
- To promote the growth of coliforms
- To isolate enteric Gram-positive bacilli
- To identify lactose fermenting and non-lactose fermenting Gram-negative bacilli (correct)
- To detect non-lactose fermenting bacteria
What color do colonies appear as if they can ferment lactose on MacConkey agar?
What color do colonies appear as if they can ferment lactose on MacConkey agar?
- Colorless
- Pink/red (correct)
- Beige
- Blue
Which component of MacConkey agar is responsible for inhibiting the growth of Gram-positive bacteria?
Which component of MacConkey agar is responsible for inhibiting the growth of Gram-positive bacteria?
- Phenol red
- Coliform bacteria
- Bile salts
- Crystal violet (correct)
Why do coliform bacteria sometimes appear surrounded by a black coloration on MacConkey agar?
Why do coliform bacteria sometimes appear surrounded by a black coloration on MacConkey agar?
Which type of bacteria are common in digestive tracts and are targeted with MacConkey agar?
Which type of bacteria are common in digestive tracts and are targeted with MacConkey agar?
Why is MacConkey agar considered a selective medium?
Why is MacConkey agar considered a selective medium?
What does pink colored growth on MacConkey agar indicate about the bacteria?
What does pink colored growth on MacConkey agar indicate about the bacteria?
Why do colonies that do not ferment lactose on MacConkey agar remain colorless?
Why do colonies that do not ferment lactose on MacConkey agar remain colorless?
What is the role of crystal violet and bile salts in MacConkey agar?
What is the role of crystal violet and bile salts in MacConkey agar?
Why is the presence of coliforms in a water supply concerning?
Why is the presence of coliforms in a water supply concerning?
What color do colonies appear as if they cannot ferment lactose on MacConkey agar?
What color do colonies appear as if they cannot ferment lactose on MacConkey agar?
What causes the pink/red color in colonies that ferment lactose on MacConkey agar?
What causes the pink/red color in colonies that ferment lactose on MacConkey agar?
Why might coliform bacteria appear surrounded by a black coloration on MacConkey agar?
Why might coliform bacteria appear surrounded by a black coloration on MacConkey agar?
What is the main purpose of using MacConkey agar in industries like food and pharmaceuticals?
What is the main purpose of using MacConkey agar in industries like food and pharmaceuticals?
Why are coliforms considered significant in terms of public health concern?
Why are coliforms considered significant in terms of public health concern?
In what way does MacConkey agar serve as a differential medium?
In what way does MacConkey agar serve as a differential medium?
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Study Notes
MacConkey Agar
- MacConkey agar is used for isolating enteric Gram-negative bacilli, such as Escherichia coli and Salmonella typhimurium.
- It is used in industries like food, dairy, cosmetic, and pharmaceutical to detect contaminated products.
- MacConkey agar is also used to detect coliforms, which are Gram-negative, lactose-fermenting bacilli common in human and animal digestive tracts.
Selective and Differential Properties
- MacConkey agar is both selective and differential.
- Its selective properties come from crystal violet and bile salts, which inhibit Gram-positive growth.
- It differentiates between lactose-fermenting and non-lactose-fermenting Gram-negatives.
Lactose Fermentation
- Pink or red coloration on MacConkey agar indicates lactose fermentation due to a pH drop and phenol red pH indicator change.
- Coliform bacteria may also have a black coloration around the colony due to bile salt precipitation from pH drop.
- Colorless or beige growth indicates no lactose fermentation.
Public Health Implications
- Presence of coliforms in a water supply can suggest fecal contamination, concerning public health officials.
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