They are Gram-positive, filamentous bacteria with branching filaments that can resemble fungi. The infection is typically indolent and is characterized by yellow “sulfur granules,” which are actually clumps of bacteria.
Clinically, it presents as granulomatous or suppurative inflammation with draining sinuses that extrude sulfur granules. Classic locations include:
Local trauma often precedes infection, helping the bacteria gain access to subcutaneous tissue. Pelvic actinomycosis has also been reported in some IUD (intrauterine device) users.
For diagnosis, the granules can be crushed between slides and Gram-stained to show a “sunray appearance.” Culture can be performed anaerobically on brain heart infusion broth or thioglycollate broth.
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