Bacterium
Actinomyces israelii
Sulfur-granule filamentous anaerobe
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High-yield clue
Yellow 'sulfur granules' draining from sinus tracts and cervicofacial 'lumpy jaw' after dental trauma are the core clues; unlike Nocardia it is anaerobic and not acid-fast.
Overview
A branching, filamentous Gram-positive anaerobe of the oral cavity that causes chronic draining sinus-tract infection. It is the classic non-acid-fast counterpart to Nocardia in coursework.
Classification
- Gram-positive
- Branching filamentous rod
- Anaerobe
- Not acid-fast
Lab & identification clues
- Sulfur granules (yellow filament colonies)
- Branching filaments on Gram stain
- Anaerobic growth
- Not acid-fast (contrast with Nocardia)
Associations
- Cervicofacial 'lumpy jaw'
- Dental trauma / poor oral hygiene
- IUD-associated pelvic study association
Commonly confused with
- Nocardia species
- Fungal hyphae
Your notes
Original student-study summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment, dosing, or specimen-handling guidance.