MBBS Microbiology

Question 1

Which organism is the most common cause of community-acquired pneumonia in adults?

Accepted Answer

Streptococcus pneumoniae

Answer

Haemophilus influenzae

Answer

Mycoplasma pneumoniae

Answer

Klebsiella pneumoniae

Question 2

Which virulence factor of Staphylococcus aureus allows it to resist phagocytosis by inhibiting opsonization?

Accepted Answer

Protein A

Answer

Leukocidin

Answer

Coagulase

Answer

Hyaluronidase

Question 3

The Ziehl-Neelsen stain is used to identify organisms that are acid-fast. Which property makes mycobacteria acid-fast?

Accepted Answer

Presence of mycolic acids in the cell wall

Answer

High peptidoglycan content

Answer

Presence of teichoic acids

Answer

Thick polysaccharide capsule

Question 4

Which hepatitis virus is transmitted via the fecal-oral route and does NOT cause chronic infection?

Accepted Answer

Hepatitis A

Answer

Hepatitis B

Answer

Hepatitis C

Answer

Hepatitis D

Question 5

Clostridium tetani produces tetanospasmin, which causes spastic paralysis. What is its mechanism of action?

Accepted Answer

Inhibits release of inhibitory neurotransmitters glycine and GABA

Answer

Blocks acetylcholine release at the neuromuscular junction

Answer

Activates adenylyl cyclase in neurons

Answer

Cleaves SNARE proteins at peripheral synapses

Question 6

Which test is used to distinguish Streptococcus pyogenes (Group A Strep) from other beta-hemolytic streptococci?

Accepted Answer

Bacitracin sensitivity

Answer

Optochin sensitivity

Answer

CAMP test

Answer

Bile solubility

Question 7

Which type of hypersensitivity reaction is the mechanism behind tuberculin skin test (Mantoux test) positivity?

Accepted Answer

Type IV (delayed-type/cell-mediated)

Answer

Type I (IgE-mediated)

Answer

Type II (cytotoxic)

Answer

Type III (immune complex)