MD - Doctor of Medicine Infectious Disease and Microbiology Questions and Answers

Question 1

A 45-year-old man with a history of a recent dental procedure followed by a prolonged course of clindamycin presents with profuse, watery, non-bloody diarrhea and lower abdominal cramping.
Stool assay is positive for toxins A and B.
What is the primary mechanism of action of these toxins produced by the causative organism?

Accepted Answer

Inactivation of Rho family GTPases, causing cytoskeletal disruption and epithelial cell death.

Answer

Activation of adenylate cyclase, leading to increased intracellular cAMP and massive fluid secretion.

Answer

Inhibition of protein synthesis by blocking the EF-2 translocation step.

Answer

Superantigen activity, leading to widespread T-cell activation and cytokine release.

Question 2

A 30-year-old female is diagnosed with her first episode of genital herpes. Which antiviral medication's mechanism of action relies on initial phosphorylation by a viral-encoded thymidine kinase, making it highly specific for infected cells?

Accepted Answer

Acyclovir

Answer

Foscarnet

Answer

Oseltamivir

Answer

Maraviroc

Question 3

A 58-year-old male with acute myeloid leukemia is undergoing induction chemotherapy and develops profound neutropenia. He becomes febrile and develops pleuritic chest pain and a cough productive of blood-streaked sputum. A high-resolution CT scan of the chest reveals several nodules, one of which has a surrounding area of ground-glass opacity. This radiologic finding is known as the halo sign. Which of the following is the most likely causative organism?

Accepted Answer

Aspergillus fumigatus

Answer

Pneumocystis jirovecii

Answer

Candida albicans

Answer

Mycobacterium tuberculosis

Question 4

A 65-year-old woman is brought to the emergency department from a nursing home with a suspected urinary tract infection. She is lethargic, her blood pressure is 85/45 mmHg despite a 1-liter crystalloid bolus, and her serum lactate is 5.0 mmol/L. According to the Surviving Sepsis Campaign's 'Hour-1 Bundle', which of the following is a critical and time-sensitive intervention that must be initiated immediately?

Accepted Answer

Obtaining blood cultures and administering broad-spectrum antibiotics

Answer

Administering intravenous hydrocortisone

Answer

Placing a central venous catheter for CVP monitoring

Answer

Initiating continuous renal replacement therapy

Question 5

A 35-year-old patient with a known history of HIV, non-adherent to antiretroviral therapy, presents with a new-onset seizure. His CD4 count is 48 cells/µL. A contrast-enhanced MRI of the brain reveals multiple ring-enhancing lesions, primarily located in the basal ganglia. What is the most likely diagnosis?

Accepted Answer

Cerebral Toxoplasmosis

Answer

Primary CNS lymphoma

Answer

Progressive Multifocal Leukoencephalopathy (PML)

Answer

Cryptococcoma

Question 6

A 22-year-old male presents to a sexual health clinic with a two-day history of purulent urethral discharge and dysuria. A Gram stain is performed on a smear of the discharge. Which of the following microscopic findings would be most diagnostic for Neisseria gonorrhoeae infection in this patient?

Accepted Answer

Gram-negative diplococci located within neutrophils

Answer

Gram-positive cocci in chains

Answer

Gram-negative rods arranged in a 'school of fish' pattern

Answer

Absence of organisms but numerous polymorphonuclear leukocytes