Question 1

What is the primary mechanism by which UV light kills bacteria?

Accepted Answer

By causing the formation of thymine dimers in DNA

Question 2

What is the main purpose of using UV light in a microbiology laboratory?

Accepted Answer

To sterilize surfaces by damaging microbial DNA

Question 3

Which of the following best describes a thymine dimer?

Accepted Answer

A covalent bond formed between two adjacent thymine bases in DNA

Question 4

Why is Mueller-Hinton agar used in antimicrobial susceptibility testing?

Accepted Answer

It allows for uniform diffusion of antibiotics

Question 5

A bacterial culture is exposed to UV light and then plated. Colonies fail to grow in the exposed area. What is the most likely explanation?

Accepted Answer

UV light caused DNA damage, preventing replication

Question 6

How is the zone of inhibition measured in an antimicrobial susceptibility test?

Accepted Answer

By measuring the diameter of the clear area around the antibiotic disk in millimeters

Question 7

Which of the following results indicates that a bacterium is resistant to an antibiotic in a disk diffusion test?

Accepted Answer

A small or nonexistent zone of inhibition

Question 8

What is the significance of a thymine dimer in bacterial DNA?

Accepted Answer

It disrupts DNA replication and transcription

Question 9

A student performs an antimicrobial susceptibility test and observes a 20 mm zone of inhibition. According to the standards, this bacterium is classified as:

Accepted Answer

Sensitive

Question 10

Which of the following equations would you use to calculate the area of the zone of inhibition if the diameter is known?

Accepted Answer

$$A = \pi r^2$

Question 11

Why might a bacterium show an intermediate response to an antibiotic in a susceptibility test?

Accepted Answer

The bacterium has partial resistance mechanisms

Question 12

Which of the following best explains why UV light is not effective for sterilizing large volumes of liquid?

Accepted Answer

UV light has poor penetrating power

Question 13

A hospital uses UV light to disinfect operating rooms. What is a limitation of this method?

Accepted Answer

UV light cannot penetrate dust or organic matter

Question 14

Which of the following is NOT a possible outcome in an antimicrobial susceptibility test?

Accepted Answer

Enhanced bacterial growth

Question 15

If a bacterium repairs UV-induced thymine dimers using photoreactivation, which enzyme is involved?

Accepted Answer

Photolyase

Control of Microbial Growth: UV Light and Antimicrobial Susceptibility Testing

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