Question 1

Which of the following best explains why the lower respiratory system is typically sterile under normal conditions?

Accepted Answer

Alveolar macrophages actively phagocytose and destroy invading microorganisms.

Question 2

A patient presents with a sore throat, fever, and a gray membrane in the throat. Gram-positive rods without endospores are cultured from the membrane. What is the most likely diagnosis?

Accepted Answer

Diphtheria

Question 3

Which of the following is a key virulence factor of Streptococcus pyogenes in causing streptococcal pharyngitis?

Accepted Answer

Streptolysins that are cytotoxic to host cells

Question 4

Which test is used to determine immunity to diphtheria?

Accepted Answer

Schick test

Question 5

A child presents with a red, sore throat, fever, and a 'strawberry tongue.' A pink-red rash develops later. Which toxin is responsible for these symptoms?

Accepted Answer

Erythrogenic toxin

Question 6

Which of the following statements about the DTaP vaccine is correct?

Accepted Answer

It contains inactivated toxins (toxoids) for diphtheria and tetanus, and acellular fragments for pertussis.

Question 7

Which of the following best describes the pathogenesis of tuberculosis in the lungs?

Accepted Answer

Bacteria multiply in macrophages, leading to the formation of a caseous center and possible calcification.

Question 8

Which diagnostic test is preferred for detecting tuberculosis in a person who has received the BCG vaccine?

Accepted Answer

Blood test measuring IFN-γ release

Question 9

A 27-year-old man with asthma is hospitalized with fever and cough. Gram-positive diplococci are cultured from his blood. Which organism is most likely responsible?

Accepted Answer

Streptococcus pneumoniae

Question 10

Which of the following is a distinguishing feature of Mycoplasma pneumoniae compared to other bacterial pneumonia pathogens?

Accepted Answer

It lacks a cell wall and is pleomorphic.

Question 11

Which of the following best explains why Legionella pneumophila is often associated with outbreaks in places like air conditioning systems and fountains?

Accepted Answer

It grows well in water, even with low levels of chlorine.

Question 12

Which of the following statements about influenza virus is correct?

Accepted Answer

Antigenic drift involves minor mutations, allowing the virus to evade immunity.

Question 13

A worker is hospitalized for acute respiratory illness after exposure to bat droppings. Microscopy reveals ovoid yeast cells. What is the most likely diagnosis?

Accepted Answer

Histoplasmosis

Question 14

Which of the following is the most common causative agent of otitis media in children?

Accepted Answer

Streptococcus pneumoniae

Question 15

Which of the following best describes the mechanism of action of the diphtheria toxin?

Accepted Answer

It interferes with protein synthesis in host cells.

Question 16

Which of the following is a characteristic symptom of pertussis (whooping cough) during the paroxysmal stage?

Accepted Answer

Violent, prolonged coughing fits

Question 17

Which of the following treatments is most appropriate for Pneumocystis pneumonia in an immunocompromised patient?

Accepted Answer

Trimethoprim

Question 18

Which of the following is a common complication of the common cold?

Accepted Answer

Otitis media

Question 19

Which of the following statements about COVID-19 vaccines is correct?

Accepted Answer

Virus-vector vaccines use a harmless adenovirus to deliver the spike protein gene.

Question 20

Which of the following best describes the transmission of Chlamydophila psittaci, the causative agent of psittacosis?

Accepted Answer

Inhalation of bird droppings containing elementary bodies

Microbial Diseases of the Respiratory System: Structure, Pathogenesis, and Clinical Features

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