NBDE Microbiology and Pathology 2 — Questions and Answers
Question 1: Which virulence factor of Streptococcus mutans is most responsible for its adhesion to smooth tooth surfaces?
- Glucosyltransferase (GTF) (Correct answer)
- Hyaluronidase
- Streptolysin O
- M protein
Correct answer: Glucosyltransferase (GTF)
Glucosyltransferase synthesizes water-insoluble glucans that mediate S. mutans adhesion to smooth enamel surfaces.
Question 2: A patient presents with white plaques on the buccal mucosa that can be wiped off, leaving a red, bleeding base. The most likely causative organism is:
- Candida albicans (Correct answer)
- Herpes simplex virus
- Streptococcus pyogenes
- Actinomyces israelii
Correct answer: Candida albicans
Pseudomembranous candidiasis (thrush) presents as removable white plaques caused by Candida albicans overgrowth.
Question 3: The Gram-negative anaerobe most strongly associated with adult periodontitis is:
- Porphyromonas gingivalis (Correct answer)
- Actinomyces naeslundii
- Streptococcus sanguinis
- Fusobacterium nucleatum
Correct answer: Porphyromonas gingivalis
Porphyromonas gingivalis is a keystone pathogen in chronic periodontitis, producing gingipains that destroy periodontal tissue.
Question 4: A biopsy of a submandibular mass shows 'sulfur granules' surrounded by neutrophils. The causative organism is best described as:
- Filamentous Gram-positive bacterium (Correct answer)
- Encapsulated Gram-negative coccus
- Acid-fast bacillus
- Dimorphic fungus
Correct answer: Filamentous Gram-positive bacterium
Actinomyces israelii, a filamentous Gram-positive bacterium, forms sulfur granules characteristic of cervicofacial actinomycosis.
Question 5: Which type of hypersensitivity reaction is responsible for the pathogenesis of contact stomatitis from dental materials?
- Type IV (delayed-type) (Correct answer)
- Type I (immediate IgE-mediated)
- Type II (cytotoxic)
- Type III (immune complex)
Correct answer: Type IV (delayed-type)
Contact stomatitis from dental materials (e.g., nickel, eugenol) is mediated by T-lymphocytes in a Type IV delayed hypersensitivity reaction.
Question 6: A lesion biopsy shows an epithelial lining with a band of hyaline (Rushton) bodies. This finding is most consistent with:
- Radicular cyst (Correct answer)
- Dentigerous cyst
- Odontogenic keratocyst
- Nasopalatine duct cyst
Correct answer: Radicular cyst
Rushton bodies are hyaline structures found within the epithelial lining of radicular (periapical) cysts.
Question 7: Which cell type is the primary mediator of chronic granulomatous inflammation as seen in periapical granulomas?
- Macrophage/epithelioid cell (Correct answer)
- Neutrophil
- Mast cell
- Plasma cell
Correct answer: Macrophage/epithelioid cell
Granulomas are composed primarily of activated macrophages (epithelioid cells) that wall off persistent antigens.
NBDE Microbiology and Pathology 2
Which virulence factor of Streptococcus mutans is most responsible for its adhesion to smooth tooth surfaces?