Question 1

Which of the following best describes a selective medium?

Accepted Answer

A medium that contains ingredients to inhibit the growth of certain microbes while allowing others to grow.

Question 2

Blood agar is used to differentiate bacteria based on their hemolytic properties. Which type of hemolysis is characterized by a clear, colorless zone around colonies due to complete lysis of red blood cells?

Accepted Answer

Beta hemolysis

Question 3

A microbiologist is testing a bacterial isolate on Mannitol Salt Agar (MSA). The medium contains a high concentration of NaCl and phenol red. What is the primary purpose of the high salt concentration in MSA?

Accepted Answer

To select for salt-tolerant (halophilic) bacteria, such as Staphylococcus species.

Question 4

Which of the following best defines a fastidious organism?

Accepted Answer

An organism that requires special nutritional or environmental conditions for growth.

Question 5

A catalase test is performed by adding hydrogen peroxide to a bacterial colony. Which result indicates a positive catalase test?

Accepted Answer

Rapid bubbling due to the release of oxygen gas.

Question 6

Which enzyme is responsible for breaking down hydrogen peroxide into water and oxygen, as shown in the equation below?

$$2H_2O_2 \rightarrow 2H_2O + O_2$

Accepted Answer

Catalase

Question 7

MacConkey Agar (MAC) contains bile salts and crystal violet. What is the primary function of these components?

Accepted Answer

To inhibit the growth of gram-positive bacteria, allowing gram-negative bacteria to grow.

Question 8

A student observes a bacterial colony on Eosin Methylene Blue (EMB) agar with a metallic green sheen. What does this result indicate?

Accepted Answer

The organism is a strong lactose fermenter, such as Escherichia coli.

Question 9

Which of the following best describes the principle of the oxidase test?

Accepted Answer

It detects the presence of cytochrome c oxidase by observing a color change when a reagent is added.

Question 10

Phenol red is used in the Triple Sugar Iron (TSI) medium. What is its primary purpose?

Accepted Answer

To act as a pH indicator, changing color in response to acid production from sugar fermentation.

Question 11

Which of the following is NOT a component of Triple Sugar Iron (TSI) medium?

Accepted Answer

Crystal violet

Question 12

A zone of clearance is observed around an antibiotic disk on an agar plate. What does this indicate?

Accepted Answer

The bacteria are sensitive to the antibiotic; the antibiotic inhibits their growth.

Question 13

Which term best describes an agent that inhibits microbial growth but does not kill the organisms?

Accepted Answer

Microbiostatic

Question 14

Which of the following antibiotics is known to disrupt cell membrane function?

Accepted Answer

Polymyxin

Question 15

Gram-negative bacteria tend to be less sensitive to antibacterial drugs. Which structural feature is primarily responsible for this reduced sensitivity?

Accepted Answer

Presence of an outer membrane that restricts drug entry

Question 16

Which of the following is an example of an antibiotic that inhibits nucleic acid synthesis?

Accepted Answer

Rifampin

Question 17

A patient is prescribed a broad-spectrum antibiotic. Which of the following best describes a broad-spectrum antibiotic?

Accepted Answer

An antibiotic that is effective against a wide range of bacteria, both gram-positive and gram-negative.

Question 18

Which adaptation is NOT a major category of antibacterial drug resistance?

Accepted Answer

Increased permeability to the drug

Question 19

The Kirby-Bauer Antibiotic Sensitivity Test is used in clinical settings primarily to:

Accepted Answer

Assess the susceptibility of bacteria to various antibiotics for guiding treatment decisions.

Question 20

Which of the following antibiotics inhibits protein synthesis in bacteria?

Accepted Answer

Tetracycline

Microbiology Lab Test 3 Review: Media, Biochemical Tests, and Antibiotic Sensitivity

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