A 40-year-old man develops rapidly progressive painful swelling of the jaw with foul-smelling discharge following a dental extraction. Gram stain shows mixed flora including Gram-positive rods with club-shaped ends and beaded filaments in palisading arrangement. Which organism is most likely involved?
- A Actinomyces israelii ✓
- B Nocardia asteroides
- C Corynebacterium diphtheriae
- D Propionibacterium acnes
Correct answer: A. Actinomyces israelii
Explanation
Actinomyces israelii is a Gram-positive branching filamentous anaerobe that is a commensal of the oral cavity. It causes cervicofacial actinomycosis, classically after dental procedures or trauma, presenting with jaw swelling, foul-smelling discharge, and sulfur granules. The beaded filaments in palisading arrangement are characteristic. Though Actinomyces is technically Gram-positive branching (not a true coccus/rod), it is grouped with Gram-positive organisms in microbiology curricula. Nocardia is partially acid-fast and aerobic.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.