Actinomycosis is a chronic suppurative infection classically involving the cervicofacial, abdominal, or thoracic regions. Although usually confined to one anatomical area, it may spread contiguously and lead to multiple sinus-tract formations.1Actinomyces israeli, a common saprophyte of the oral cavity, is the causative organism in the human form of the disease. An anaerobic or microaerophilic branching fungus, it is morphologically identical to the aerobic Actinomyces, Nocardia asteroides.2 Even after Waksman and Henrici 3 clarified the bacteriology of the two organisms, subsequent reviewers of both actinomycosis and nocardiosis have included conditions diagnosed on morphological grounds alone.4,5 Identification is of more than academic interest, since the two organisms have generally distinct antibiotic sensitivities.6Nocardia asteroides responds best to sulfonamides and A israeli to penicillin.
Clinically, actinomycotic infections have been distinguished from nocardial infections by the following criteria: First, A israeli is reported to form sulfur granules. Second, the