Question 1

Which of the following best describes the purpose of the aseptic technique in microbiology?

Accepted Answer

To exclude contaminants when transferring bacteria to culture media

Question 2

A microbiologist wants to grow bacteria that require less oxygen. Which type of culture medium should they use?

Accepted Answer

Agar deep

Question 3

What is the main function of an inoculating loop in the laboratory?

Accepted Answer

To streak bacteria over the surface of solid media for isolation

Question 4

Why should test tubes be held at a 20-degree angle during aseptic transfer procedures?

Accepted Answer

To minimize the amount of dust that could fall into them

Question 5

Which historical figure is credited with developing solid media for bacterial isolation, enabling the observation of individual colonies?

Accepted Answer

Robert Koch

Question 6

A student performs a 10-fold serial dilution of a bacterial sample and plates 0.1 mL from the $$10^{-4}$$ dilution. After incubation, 50 colonies are counted. What is the original concentration of bacteria in CFU/mL?

Accepted Answer

$$5 	imes 10$$^{6}$$ CFU/mL

Question 7

Which technique is most appropriate for isolating pure bacterial colonies from a mixed sample?

Accepted Answer

Streak plate technique

Question 8

Which of the following statements about MacConkey agar is TRUE?

Accepted Answer

It differentiates bacteria based on lactose fermentation

Question 9

On Xylose Lysine Deoxycholate (XLD) agar, what does the appearance of red colonies with black centers indicate?

Accepted Answer

Presence of Salmonella species

Question 10

Which medium is specifically designed to isolate and differentiate Vibrio species based on their ability to ferment sucrose?

Accepted Answer

TCBS agar

Question 11

A urine sample is plated on CLED agar. After incubation, yellow colonies are observed. What does this indicate?

Accepted Answer

The bacteria are lactose fermenters such as E. coli

Question 12

Which of the following best describes the difference between selective and differential media?

Accepted Answer

Selective media inhibit unwanted bacteria, while differential media distinguish bacteria based on metabolic properties

Question 13

Which anaerobic medium is commonly used to grow obligate anaerobes in the laboratory?

Accepted Answer

Robertson's cooked meat medium

Question 14

In the pour plate method, why are some bacterial colonies found inside the agar rather than only on the surface?

Accepted Answer

The sample is mixed with molten agar before solidification

Question 15

Which of the following best explains why a streak plate is used in clinical microbiology labs?

Accepted Answer

To isolate individual colonies for pure culture

Question 16

A microbiologist observes colorless colonies on MacConkey agar. What does this indicate about the bacteria?

Accepted Answer

They are non-lactose fermenters

Question 17

Which of the following equations correctly calculates the original concentration of bacteria (CFU/mL) after plating 0.1 mL of a $$10^{-3}$$ dilution and counting 80 colonies?

Accepted Answer

$$80 	imes 10$$^{4}$$ CFU/mL

Question 18

Which of the following is a key reason for using thioglycolate broth in microbiology?

Accepted Answer

To grow anaerobic bacteria

Question 19

Which of the following best describes the function of bile salts in MacConkey agar?

Accepted Answer

They inhibit the growth of Gram-positive bacteria

Aseptic Technique, Bacterial Transfer, and Culture Media in Microbiology

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