Question 1

Which of the following is the primary virulence factor of Streptococcus pneumoniae that allows it to evade phagocytosis and is the main target of conjugate vaccines?

Accepted Answer

Polysaccharide capsule

Question 2

A 3-year-old child presents with fever, irritability, and a bulging fontanelle. Gram stain of cerebrospinal fluid reveals Gram-positive diplococci. Which pathogen is most likely responsible?

Accepted Answer

Streptococcus pneumoniae

Question 3

Which of the following best explains why the polysaccharide vaccine for Streptococcus pneumoniae was phased out in favor of conjugate vaccines?

Accepted Answer

Conjugate vaccines induce a T-cell dependent response, leading to immunologic memory.

Question 4

A patient with a history of splenectomy is at increased risk for severe disease from which of the following pathogens due to impaired clearance of encapsulated bacteria?

Accepted Answer

Streptococcus pneumoniae

Question 5

Which of the following statements about Neisseria meningitidis serogroup B (MenB) is correct?

Accepted Answer

MenB is poorly immunogenic due to molecular mimicry with human glycans.

Question 6

Which of the following is a key mechanism by which Mycobacterium tuberculosis survives within host macrophages?

Accepted Answer

Inhibition of phagosome-lysosome fusion

Question 7

A 6-month-old infant develops a severe cough with inspiratory 'whoop' and post-tussive vomiting. Which virulence factor of Bordetella pertussis is primarily responsible for the disruption of immune cell signaling?

Accepted Answer

Pertussis toxin (PT)

Question 8

Which of the following best describes the epidemiological trend of invasive pneumococcal disease (IPD) in Australia as of 2024?

Accepted Answer

IPD rates have reached a 20-year high.

Question 9

Which of the following is a major reason for the resurgence of pertussis (whooping cough) in countries with high vaccine coverage?

Accepted Answer

Switch from whole-cell to acellular vaccines leading to waning immunity

Question 10

A 25-year-old man presents with fever, headache, and a petechial rash. He rapidly deteriorates and develops disseminated intravascular coagulation (DIC). Which bacterial component is most responsible for triggering this severe inflammatory response?

Accepted Answer

Lipooligosaccharide (LOS) endotoxin

Question 11

Which of the following best explains why the Hib conjugate vaccine is more effective in infants than the original polysaccharide vaccine?

Accepted Answer

It induces a T-cell dependent immune response.

Question 12

Which of the following is the most common clinical presentation of invasive pneumococcal disease (IPD) in children under 5 years of age?

Accepted Answer

Bacteraemia

Question 13

A patient with latent tuberculosis infection (LTBI) is most likely to:

Accepted Answer

Have a positive tuberculin skin test and no symptoms

Question 14

Which of the following is a significant concern regarding the treatment of tuberculosis globally?

Accepted Answer

Emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains

Question 15

Which of the following best describes the mechanism of action of adenylate cyclase toxin (ACT) produced by Bordetella pertussis?

Accepted Answer

It converts ATP to cAMP, disrupting phagocyte function.

Question 16

Which of the following is a key reason why non-typeable Haemophilus influenzae (NTHi) has become the predominant cause of invasive H. influenzae disease in countries with established Hib vaccination programs?

Accepted Answer

NTHi lacks a capsule and is not targeted by current vaccines.

Question 17

A 4-year-old child develops acute otitis media. Which of the following statements about the causative agent is correct?

Accepted Answer

Streptococcus pneumoniae is the most common bacterial cause and is least likely to resolve spontaneously.

Question 18

Which of the following best explains why outbreaks of invasive pneumococcal disease (IPD) are rare but can have high fatality rates in certain settings?

Accepted Answer

Outbreaks occur in crowded settings with high-risk individuals, such as nursing homes or jails.

Question 19

Which of the following is a major limitation of the BCG vaccine for tuberculosis prevention?

Accepted Answer

It provides inconsistent protection against pulmonary TB in adults.

Question 20

Which of the following best describes the pathogenesis of Neisseria meningitidis leading to disseminated intravascular coagulation (DIC)?

Accepted Answer

Release of outer membrane vesicles containing LOS triggers a massive cytokine response, causing vascular damage and DIC.

Respiratory and Invasive Bacterial Pathogens: Structure, Pathogenesis, Epidemiology, and Prevention

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