MacConkey Agar

The video tutorial explains the use of MacConkey Agar, a selective and differential medium used to identify gram-negative bacteria and their ability to ferment lactose. It details the selective nature of the agar, which inhibits gram-positive bacteria, and the differential aspect, which distinguishes lactose fermenters by color change. The tutorial guides viewers through interpreting results based on growth and color, emphasizing the importance of these observations in determining bacterial characteristics.

What is the primary function of bile salts and crystal violet in MacConkey Agar?

• To enhance the color change in lactose fermentation

• To promote the growth of gram-positive organisms

• To inhibit the growth of gram-positive organisms

• To inhibit the growth of gram-negative organisms

What happens when bacteria ferment lactose on MacConkey Agar?

• The medium turns pink

• The medium turns green

• The medium turns blue

• The medium remains colorless

If there is no growth on MacConkey Agar, what can be inferred about the organism?

• It is gram-negative

• It is lactose positive

• It is gram-positive

• It is lactose negative

How can you determine if an organism is lactose positive on MacConkey Agar?

• The colonies are green

• The colonies are pink

• The colonies are tan

• The colonies are blue

What does a tan color around colonies on MacConkey Agar indicate?

• Lactose negative

• Gram-positive

• Lactose positive

• Gram-negative

What is the first step in interpreting MacConkey Agar results?

• Determining if there is growth

• Observing the color change

• Checking the pH level

• Measuring the colony size

What does a pink color around colonies on MacConkey Agar signify?

• Lactose positive

• Lactose negative

• Gram-positive

• No growth