Microbiology: MacConkey Agar

Microbiology: MacConkey Agar

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Science, Chemistry, Biology

University

Hard

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The video tutorial explains the use of MacConkey Agar, a selective and differential medium, to identify gram-negative bacteria capable of fermenting lactose into lactic acid. The presence of bile salts and crystal violet inhibits gram-positive bacteria, allowing only gram-negative bacteria to grow. The medium contains a pH indicator that turns hot pink when lactose is fermented into acid end products. The biochemical pathway involves lactose being hydrolyzed into glucose and galactose, which enter glycolysis to form pyruvate, eventually converting to lactic acid. The video also covers interpreting results on MacConkey Agar plates, identifying lactose fermenting and non-fermenting colonies.

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5 questions

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1.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

What is the primary purpose of MacConkey Agar in bacterial culture?

To promote the growth of gram-positive bacteria

To select for gram-negative bacteria and differentiate lactose fermenters

To differentiate between aerobic and anaerobic bacteria

To identify bacterial spores

2.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Which component in MacConkey Agar is responsible for indicating lactose fermentation?

Lactate dehydrogenase

pH indicator

Crystal violet

Bile salts

3.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

What are the monosaccharides produced from the hydrolysis of lactose?

Fructose and sucrose

Glucose and galactose

Maltose and ribose

Lactose and sucrose

4.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Which enzyme converts pyruvate into lactic acid during lactose fermentation?

Lactate dehydrogenase

Beta-galactosidase

Amylase

Protease

5.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

How can you identify non-lactose fermenting colonies on MacConkey Agar?

They turn the agar black

They produce a green sheen

They appear colorless or pale

They appear hot pink