Question 1

Which of the following best describes a 'selective medium' in microbiology?

Accepted Answer

A medium that contains one or more agents that inhibit the growth of certain microbes while encouraging the growth of others.

Question 2

A microbiologist wants to isolate a single species of bacteria from a mixed sample. Which technique should they use?

Accepted Answer

Streak plate method

Question 3

Which of the following statements about agar is TRUE?

Accepted Answer

Agar is not digested by most microbes and remains solid at incubation temperatures up to 100$$^\circC.$$

Question 4

A clinical specimen is obtained from a patient's blood. Which term best describes this type of sample?

Accepted Answer

Clinical specimen

Question 5

Which of the following best describes a 'differential medium'?

Accepted Answer

A medium that allows multiple types of organisms to grow but displays visible differences among them, such as color changes.

Question 6

During incubation, why might a microbiologist need to adjust the atmospheric gases in the incubator?

Accepted Answer

Some microbes require specific gases such as oxygen or carbon dioxide for optimal growth.

Question 7

Which of the following is a key difference between defined (synthetic) and complex media?

Accepted Answer

Defined media have a precisely known chemical composition, while complex media contain at least one ingredient that is not chemically defined.

Question 8

A microbiologist is using MacConkey agar to culture bacteria from a stool sample. What is the primary function of this medium?

Accepted Answer

It is both selective and differential, allowing the growth of Gram-negative bacteria and distinguishing lactose fermenters.

Question 9

Which of the following best describes the function of an incubator in a microbiology laboratory?

Accepted Answer

It provides controlled temperature and atmospheric conditions to encourage microbial growth.

Question 10

A scientist wants to grow only Staphylococcus aureus from a mixed sample. Which type of medium should they use?

Accepted Answer

Selective medium

Question 11

Which of the following is NOT a correct description of a pure culture?

Accepted Answer

A culture containing two or more species of microorganisms.

Question 12

Why is gelatin not commonly used as a solidifying agent in microbiological media?

Accepted Answer

Gelatin is digested by many microbes and melts at temperatures below 37$$^\circC.$$

Question 13

Which of the following best describes an enriched medium?

Accepted Answer

A medium that contains complex organic substances such as blood, serum, or special growth factors for fastidious microbes.

Question 14

A microbiologist observes that a bacterial colony changes the color of the medium on a differential agar plate. What does this indicate?

Accepted Answer

The bacterium has a metabolic property that interacts with the medium, causing a visible change.

Question 15

Which of the following is a correct sequence of the 'Five I's' in microbiology laboratory techniques?

Accepted Answer

Inoculation, incubation, isolation, inspection, identification

Question 16

A scientist is preparing a medium with the following composition: 10 g glucose, 5 g NaCl, 2 g K$$_2$$HPO$$_4$$, and 1 g MgSO$$_4$$ per liter of water. What type of medium is this?

Accepted Answer

Defined (synthetic) medium

Question 17

Which of the following best explains why a microbiologist would use a solid medium rather than a liquid medium?

Accepted Answer

Solid media allow for the isolation of individual colonies from a mixed sample.

Question 18

A contaminated culture is best defined as:

Accepted Answer

A culture that was once pure or mixed but now contains unwanted microbes.

Question 19

Which of the following is a real-world example of using a selective and differential medium in clinical diagnostics?

Accepted Answer

Using MacConkey agar to isolate and differentiate Gram-negative enteric bacteria from a stool sample.

Laboratory Methods for Studying Microbes: Culture Media and Isolation Techniques

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