Q: Which of the following equations best represents the calculation of plaque-forming units (PFUs) in a bacteriophage assay?

$$ \text{PFU} = \frac{\text{Number of plaques}}{\text{Volume plated (mL)}} $$

Question 1

Which of the following statements best explains why antibiotics are ineffective against viruses?

Accepted Answer

Viruses do not possess metabolic pathways or ribosomes, which are the targets of antibiotics.

Question 2

A scientist is culturing bacteriophages in the laboratory. After mixing the phages with bacteria and plating them on agar, clear zones appear. What do these clear zones represent?

Accepted Answer

Plaques, which are areas where bacteriophages have lysed the bacteria.

Question 3

Which of the following best describes the difference between enveloped and non-enveloped viruses regarding their resistance to disinfectants?

Accepted Answer

Non-enveloped viruses are more resistant to disinfectants because they lack a lipid envelope.

Question 4

A patient presents with severe diarrhea. Laboratory tests confirm the presence of rotavirus. Which transmission route is most likely responsible for this infection?

Accepted Answer

Fecal-oral route

Question 5

During the lysogenic cycle of a bacteriophage, which of the following occurs?

Accepted Answer

Viral DNA integrates into the host genome and remains dormant as a prophage.

Question 6

Which virus is most associated with the risk of cervical cancer, and what is the recommended prevention strategy?

Accepted Answer

HPV (especially types 16 and 18); vaccination

Question 7

A virus is described as having a nucleic acid core, a capsid, and sometimes an envelope. What is the term for the complete infectious virus particle?

Accepted Answer

Virion

Question 8

Which of the following best explains the process of antigenic shift in influenza viruses?

Accepted Answer

Major genetic changes resulting in new virus strains and pandemics.

Question 9

A patient is diagnosed with hepatitis B. Which laboratory test is most appropriate for confirming the infection?

Accepted Answer

HBsAg antigen test

Question 10

Which of the following viruses uses reverse transcriptase to convert its RNA genome into DNA, which then integrates into the host genome?

Accepted Answer

HIV

Question 11

A child presents with a rash and Koplik spots. Which virus is most likely responsible, and what is the recommended prevention?

Accepted Answer

Measles virus; MMR vaccine

Question 12

Which of the following is a unique characteristic of prions compared to viruses?

Accepted Answer

Prions are infectious proteins with no nucleic acid.

Question 13

A laboratory technician is using PCR to identify a viral infection. What is the primary target of this technique?

Accepted Answer

Viral nucleic acid

Question 14

Which of the following best describes the function of viral spikes found on the envelope?

Accepted Answer

They assist in attachment to host cells.

Question 15

A patient is exposed to rabies virus via an animal bite. What is the most effective post-exposure intervention?

Accepted Answer

Immediate vaccination

Question 16

Which of the following equations best represents the calculation of plaque-forming units (PFUs) in a bacteriophage assay?

Accepted Answer

$$ 	ext{PFU} = \frac{	ext{Number of plaques}}{	ext{Volume plated (mL)}} $$

Question 17

A virus infects a host cell and immediately begins producing viral proteins and assembling new virions, resulting in cell lysis. Which cycle is this describing?

Accepted Answer

Lytic cycle

Question 18

Which of the following viruses is most likely to cause severe bronchitis and pneumonia in infants, and what is the recommended prevention?

Accepted Answer

RSV; hygiene practices

Question 19

A patient with chronic liver disease is found to have hepatitis C. Which laboratory test is most appropriate for diagnosis?

Accepted Answer

ELISA for antibodies

Question 20

Which of the following best describes the process of viral uncoating in animal viruses?

Accepted Answer

Enzymatic removal of the capsid to release viral nucleic acid

Chapter 13: Viruses – Structure, Classification, and Human Diseases

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