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Microbiology & Immunology Flashcards

6 cards from real USMLE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 6 Microbiology & Immunology flashcards as text

  1. A sputum culture grows gram-positive cocci in clusters that are catalase-positive and coagulase-positive. What organism is this?

    Answer: Staphylococcus aureus

    Coagulase-positive Staphylococcus aureus is distinguished from other staphylococci by its production of coagulase, which converts fibrinogen to fibrin.

  2. Which type of T helper cell is responsible for orchestrating the response against intracellular pathogens by activating macrophages through IFN-gamma?

    Answer: Th1

    Th1 cells produce IFN-gamma and TNF-beta, activating macrophages to destroy intracellular pathogens and driving cell-mediated immunity.

  3. A child is vaccinated with a live attenuated vaccine. Why is this vaccine contraindicated in immunocompromised patients?

    Answer: The attenuated virus can revert to virulence and cause disease in immunocompromised hosts

    Live attenuated vaccines can cause disease in immunocompromised patients because the attenuated organism may revert to virulence when the immune system cannot control even weakened pathogens.

  4. A CSF sample shows gram-negative diplococci. What is the most likely causative organism in an 18-year-old college student?

    Answer: Neisseria meningitidis

    Neisseria meningitidis is the most common cause of bacterial meningitis in adolescents and young adults, particularly in close-contact settings like college dormitories.

  5. Which mechanism allows bacteria to acquire antibiotic resistance from the environment by taking up naked DNA?

    Answer: Transformation

    Transformation is the uptake of naked DNA from the environment by naturally competent bacteria, allowing acquisition of resistance genes from dead bacteria.

  6. A positive tuberculin skin test (PPD) indicates which type of hypersensitivity reaction?

    Answer: Type IV (delayed-type hypersensitivity, T-cell mediated)

    PPD reaction is a Type IV delayed-type hypersensitivity reaction mediated by sensitized memory T cells that recognize tuberculin antigens and recruit macrophages, peaking at 48-72 hours.