Question 1

Which of the following best describes the difference between bacteriostatic and bactericidal antibiotics?

Accepted Answer

Bacteriostatic antibiotics inhibit bacterial growth, while bactericidal antibiotics kill bacteria.

Question 2

A patient is prescribed an antibiotic for a bacterial infection. The minimum concentration needed to inhibit bacterial growth is $$0.5\ \mathrm{mg/mL}$$, and the minimum concentration needed to kill the bacteria is $$2.0\ \mathrm{mg/mL}. $$Which statement is correct regarding the agent's classification?

Accepted Answer

The agent is bacteriostatic because $$\mathrm{MIC} is $$much lower than $$\mathrm{MBC}.$$

Question 3

Which factor does NOT affect the results of the Kirby-Bauer disk diffusion method?

Accepted Answer

Ability to distinguish between bacteriostatic and bactericidal drugs

Question 4

Why is the McFarland standard used in the disk diffusion (Kirby-Bauer) method?

Accepted Answer

To standardize the density of the bacterial inoculum for reproducible results

Question 5

Which of the following is a correct sequence in the five stages of biofilm formation?

Accepted Answer

Attachment, EPS matrix production, maturation, dispersal, planktonic release

Question 6

Which statement best explains why endospores are highly resistant to environmental stress?

Accepted Answer

Endospores contain high levels of small acid-soluble proteins (SASPs) that bind DNA and protect it from UV damage.

Question 7

A chemical agent causes deamination of cytosine in DNA. What is the most likely mutation that will result after DNA replication?

Accepted Answer

A cytosine-to-uracil transition, which pairs with adenine, leading to a C-G to T-A mutation

Question 8

Which DNA repair mechanism uses the cell’s energy in the form of ATP to remove damaged DNA and fill the gap using the opposite strand as a template?

Accepted Answer

Nucleotide Excision Repair (NER)

Question 9

Which wavelength range is considered optimal for germicidal effects in UV radiation?

Accepted Answer

$$260-265\ \mathrm{nm}$$

Question 10

What is the primary effect of UV radiation on bacterial DNA?

Accepted Answer

It creates photoproducts such as thymine dimers, which block DNA polymerase.

Question 11

Which of the following statements about endospore formation is correct?

Accepted Answer

Endospores are formed when bacteria encounter unfavorable conditions such as nutrient depletion.

Question 12

A bacterial cell is exposed to UV light and forms a thymine dimer. Which repair mechanism uses visible light to activate an enzyme that breaks the covalent bond between the thymine bases?

Accepted Answer

Photoactivation (photoreactivation)

Question 13

Which of the following is TRUE regarding vertical and horizontal gene transfer in bacteria?

Accepted Answer

Horizontal gene transfer allows bacteria to acquire new genetic material from other organisms, not just from parent to offspring.

Question 14

During bacterial conjugation, what is the role of the F plasmid?

Accepted Answer

It mediates the transfer of genetic material between bacteria via direct cell-to-cell contact.

Question 15

A bacterial cell receives an F'128 plasmid containing genes for chloramphenicol resistance (Cat) and lactose fermentation. Which medium would allow you to select for cells that have acquired both traits?

Accepted Answer

MacConkey agar with chloramphenicol

Question 16

Which of the following statements about transformation in bacteria is correct?

Accepted Answer

Competent cells can acquire DNA from their environment, which can be induced chemically or occur naturally.

Question 17

In a pGlo transformation experiment, which condition is necessary for the bacteria to express the green fluorescent protein (GFP) gene?

Accepted Answer

Presence of arabinose sugar in the medium

Question 18

Which structure in the endospore is responsible for enzymatic and chemical resistance?

Accepted Answer

Spore coat

Question 19

Which of the following is a correct description of antiseptics?

Accepted Answer

Antiseptics are used on living tissue and can affect living cells at high doses.

Question 20

A student is testing the MIC of an antibiotic using serial dilutions. If the last tube showing no growth contains $$0.125\ \mathrm{mg/mL} of $$antibiotic, what is the MIC?

Accepted Answer

$$0.125\ \mathrm{mg/mL}$$

Microbiology Lab Practical 2 Study Guide: Antibiotic Resistance, Biofilms, DNA Damage & Repair, and Genetic Exchange

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