Question 1

Which of the following best describes the primary function of a selective medium, as illustrated in the first image?

Accepted Answer

To inhibit the growth of certain microorganisms while allowing others to grow.

Question 2

A microbiologist wants to isolate a specific bacterium from a mixed sample. Which type of medium should they use based on the images and study materials?

Accepted Answer

Selective medium

Question 3

Which of the following statements about differential media is correct, according to the second image and your study materials?

Accepted Answer

Differential media allow all species to grow but distinguish them based on observable traits.

Question 4

A plate shows colonies with different colors after incubation. What type of medium was most likely used?

Accepted Answer

Differential medium

Question 5

Which of the following best explains why a selective medium might be used in a clinical laboratory?

Accepted Answer

To isolate a pathogen from a mixed microbial population by inhibiting non-target organisms.

Question 6

Which of the following is an example of a medium that is both selective and differential, as described in the study materials?

Accepted Answer

Eosin Methylene Blue (EMB) agar

Question 7

A microbiologist observes that all colonies on a plate look similar, regardless of the species present. What type of medium is most likely being used?

Accepted Answer

General-purpose non-differential medium

Question 8

Which of the following best describes the role of phenol red in a differential medium?

Accepted Answer

It serves as a pH indicator to detect acid production from fermentation.

Question 9

If a bacterium ferments lactose on EMB agar, what result would you expect to see?

Accepted Answer

Colonies with a metallic green sheen.

Question 10

Which equation best represents the fermentation of glucose by bacteria, as detected in a phenol red broth test?

Accepted Answer

$$\mathrm{C_6H_{12}O_6$} \rightarrow 2\ \mathrm{C_3H_6O_3}$$

Question 11

A microbiologist streaks a mixed sample onto a medium and observes that only one type of colony grows. What is the most likely explanation?

Accepted Answer

The medium is selective.

Question 12

Which of the following best describes why blood agar is considered a differential medium?

Accepted Answer

It allows for the visual distinction of bacteria based on hemolysis.

Question 13

A student observes blackening of bile esculin agar after inoculation with a bacterial sample. What does this indicate?

Accepted Answer

The bacterium can hydrolyze esculin in the presence of bile.

Question 14

Which of the following best explains why MSA (Mannitol Salt Agar) is both selective and differential?

Accepted Answer

It contains mannitol for fermentation and a high salt concentration to select for salt-tolerant microbes.

Question 15

Which of the following scenarios best illustrates the use of a differential medium in a clinical setting?

Accepted Answer

A lab technician wants to distinguish between lactose-fermenting and non-lactose-fermenting bacteria in a urine sample.

Question 16

Which of the following best describes the outcome when a bacterium utilizes peptone instead of fermenting carbohydrate in a phenol red broth test?

Accepted Answer

The medium turns pink or magenta due to ammonia production.

Selective and Differential Media & Biochemical Tests in Microbiology

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