MBBS Microbiology 2

Question 1

Which fungal infection is most commonly seen in immunocompromised patients and presents with a 'soap bubble' appearance on brain imaging?

Accepted Answer

Cryptococcosis

Answer

Cryptococcus neoformans causes cryptococcal meningitis in immunocompromised patients; the mucoid capsule produces the 'soap bubble' lesions seen on CT/MRI of the brain.

Question 2

A patient presents with rice-water stools and severe dehydration. The causative organism produces a toxin that permanently activates Gs protein. Which organism is responsible?

Accepted Answer

Vibrio cholerae

Answer

Vibrio cholerae produces cholera toxin that permanently ADP-ribosylates Gs alpha subunit, leading to constitutive activation of adenylyl cyclase, massive chloride secretion, and rice-water diarrhea.

Question 3

Which antibiotic acts by inhibiting bacterial cell wall synthesis by binding to the D-Ala-D-Ala terminus of peptidoglycan precursors?

Accepted Answer

Vancomycin

Answer

Vancomycin binds to the D-Ala-D-Ala terminus of peptidoglycan precursors, preventing transglycosylation and transpeptidation, thereby inhibiting cell wall synthesis.

Question 4

A 3-year-old presents with a 'barking cough' and inspiratory stridor. Which virus is the most common cause of this condition (croup)?

Accepted Answer

Parainfluenza virus

Answer

Parainfluenza virus type 1 is the most common cause of croup (laryngotracheobronchitis), characterized by subglottic edema producing the classic barking cough and inspiratory stridor.

Question 5

Which organism causes 'walking pneumonia' and lacks a cell wall, making it intrinsically resistant to beta-lactam antibiotics?

Accepted Answer

Mycoplasma pneumoniae

Answer

Mycoplasma pneumoniae lacks a cell wall entirely, making it resistant to all beta-lactam antibiotics; it causes atypical 'walking pneumonia' with mild symptoms and a dry cough.

MBBS - Bachelor of Medicine and Bachelor of Surgery Practice Test

MBBS - Bachelor of Medicine and Bachelor of Surgery Practice Test

MBBS Microbiology 2