NBDE Microbiology and Pathology 5 — Questions and Answers
Question 1: A Gram-positive, catalase-negative coccus that is optochin-sensitive and bile-soluble is best identified as:
- Streptococcus pneumoniae (Correct answer)
- Streptococcus viridans
- Enterococcus faecalis
- Staphylococcus aureus
Correct answer: Streptococcus pneumoniae
S. pneumoniae is uniquely optochin-sensitive and bile-soluble, distinguishing it from other alpha-hemolytic streptococci.
Question 2: Which mediator released by mast cells causes immediate vasodilation and increased vascular permeability in acute inflammation?
- Histamine (Correct answer)
- Leukotriene B4
- Prostaglandin E2
- Tumor necrosis factor
Correct answer: Histamine
Histamine is preformed in mast cell granules and is released immediately upon IgE cross-linking, causing rapid vasodilation and increased permeability.
Question 3: A central giant cell granuloma of the jaw is best distinguished from a giant cell tumor of bone by which feature?
- Location in the jaw anterior to the first molar and patient age (Correct answer)
- Presence of multinucleated giant cells
- Vascular stroma between giant cells
- Response to curettage
Correct answer: Location in the jaw anterior to the first molar and patient age
CGCG typically occurs in the jaw anterior to the first molar in patients under 30, whereas giant cell tumor of bone affects epiphyses of long bones in older adults.
Question 4: Necrotizing ulcerative gingivitis (NUG) is most characteristically associated with which combination of organisms?
- Fusobacterium nucleatum and Treponema vincentii (Correct answer)
- Porphyromonas gingivalis and Tannerella forsythia
- Actinomyces israelii and Streptococcus mutans
- Prevotella intermedia and Aggregatibacter actinomycetemcomitans
Correct answer: Fusobacterium nucleatum and Treponema vincentii
NUG (Vincent's angina) is caused by a fusospirochetal complex of Fusobacterium nucleatum and Treponema vincentii in stressed or immunocompromised patients.
Question 5: A painless, fluctuant, blue-domed swelling on the floor of the mouth that transilluminates is most consistent with:
- Ranula (Correct answer)
- Mucocele
- Dermoid cyst
- Ludwig angina
Correct answer: Ranula
A ranula is a mucus retention or extravasation cyst of the sublingual or submandibular gland, presenting as a blue-domed, transilluminant swelling on the floor of the mouth.
Question 6: Which oncogene product is most commonly mutated in squamous cell carcinoma of the oral cavity?
- p53 tumor suppressor (Correct answer)
- KRAS proto-oncogene
- HER2/neu
- BCL-2
Correct answer: p53 tumor suppressor
p53 mutations are the most frequent genetic alterations in oral squamous cell carcinoma, often induced by tobacco carcinogens and HPV E6 protein.
Question 7: A 35-year-old HIV-positive patient presents with a unilateral, white, corrugated lesion on the lateral tongue that cannot be wiped off. The most likely diagnosis is:
- Hairy leukoplakia (Correct answer)
- Oral candidiasis
- Lichen planus
- Leukoplakia
Correct answer: Hairy leukoplakia
Oral hairy leukoplakia is caused by Epstein-Barr virus and presents as non-removable, corrugated white plaques on the lateral tongue border in immunocompromised patients.
NBDE Microbiology and Pathology 5
A Gram-positive, catalase-negative coccus that is optochin-sensitive and bile-soluble is best identified as: