MBBS Microbiology

Question 1

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

Accepted Answer

Streptococcus pneumoniae

Answer

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia in adults, accounting for approximately 30-70% of cases.

Question 2

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

Accepted Answer

Protein A

Answer

Protein A binds to the Fc region of IgG antibodies, preventing opsonization and thereby inhibiting phagocytosis by neutrophils.

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

Mycolic acids are long-chain fatty acids in the mycobacterial cell wall that retain the carbol fuchsin dye even after acid-alcohol decolorization.

Question 4

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

Accepted Answer

Hepatitis A

Answer

Hepatitis A virus is transmitted fecal-orally and causes only acute self-limiting infection, never leading to chronic hepatitis or carrier state.

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

Tetanospasmin cleaves synaptobrevin (a SNARE protein) in inhibitory interneurons, blocking release of glycine and GABA, resulting in unopposed motor neuron excitation and spastic paralysis.

MBBS - Bachelor of Medicine and Bachelor of Surgery Practice Test

MBBS - Bachelor of Medicine and Bachelor of Surgery Practice Test

MBBS Microbiology