Practice Test GeeksNBME Practice Test
← All NBME Flashcard Decks

Microbiology Flashcards

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

Read the first 7 Microbiology flashcards as text

  1. A 4-year-old presents with a barking cough and inspiratory stridor. The causative virus replicates in respiratory epithelium and has a negative-sense, single-stranded RNA genome with a helical nucleocapsid. Which virus family does this pathogen belong to?

    Answer: Paramyxoviridae

    Parainfluenza virus, the most common cause of croup (laryngotracheobronchitis), belongs to Paramyxoviridae and has a negative-sense ssRNA genome with helical symmetry.

  2. A retrovirus integrates its genome into the host cell's DNA. Which enzyme is responsible for converting the viral RNA genome into double-stranded DNA prior to integration?

    Answer: Reverse transcriptase

    Reverse transcriptase (RNA-dependent DNA polymerase) copies the viral ssRNA into cDNA and then synthesizes the complementary strand to form dsDNA.

  3. A patient with AIDS presents with ring-enhancing lesions in the brain on MRI. CSF India ink preparation is negative. Brain biopsy shows tissue cysts containing bradyzoites. Which organism is responsible?

    Answer: Toxoplasma gondii

    Toxoplasma gondii reactivation in AIDS causes multiple ring-enhancing lesions with bradyzoite-containing tissue cysts; India ink highlights Cryptococcus, not Toxoplasma.

  4. A hepatitis virus has a partially double-stranded circular DNA genome and replicates via an RNA intermediate using a viral reverse transcriptase. Which hepatitis virus has this replication strategy?

    Answer: Hepatitis B virus

    Hepatitis B virus (HBV) is a hepadnavirus with a partially dsDNA genome; it replicates through an RNA pregenome intermediate using reverse transcriptase, making it targetable by nucleoside analogs.

  5. A 22-year-old college student develops fever, pharyngitis, and posterior cervical lymphadenopathy. A peripheral blood smear shows atypical lymphocytes. The heterophile antibody test is positive. Which cell type is the primary reservoir for the causative virus?

    Answer: B lymphocytes

    Epstein-Barr virus (EBV) infects B lymphocytes via CD21 (complement receptor 2); the atypical lymphocytes seen on smear are reactive cytotoxic T cells responding to infected B cells.

  6. Interferons are produced by virally infected cells and provide antiviral protection by which primary mechanism?

    Answer: Inducing 2'-5' oligoadenylate synthetase and PKR to degrade viral RNA and inhibit translation

    Type I interferons (IFN-α/β) induce enzymes such as 2'-5' oligoadenylate synthetase (activating RNase L) and PKR, which degrade viral RNA and halt protein synthesis in infected and neighboring cells.

  7. A neonate develops encephalitis and diffuse vesicular skin lesions. The mother had no active lesions at delivery. The causative virus establishes latency in the dorsal root ganglia and is a double-stranded DNA virus with an icosahedral capsid surrounded by a tegument and envelope. Which virus is responsible?

    Answer: Herpes simplex virus type 2

    Neonatal herpes is most often caused by HSV-2 acquired during passage through an infected birth canal, even without visible maternal lesions; it causes encephalitis and disseminated vesicular lesions.