Final Diagnosis -- Actinomyces Israelii and Haemophilus (Actinobacillus) Actinomycetemcomitans infection




The patient was taken to surgery, and the thoracic and soft tissue components of the infection were debrided, and the patient was discharged on a 4-6 week course of IV ampicillin. Due to an allergic reaction, the patient was switched to ceftriaxone. He was seen four weeks post-operatively and had complete resolution of his physical findings and systemic symptoms. The plan was to continue IV antibiotic therapy, and then switch to an oral course of approximately one year.


Actinomyces species are slow-growing gram-positive filamentous rod with a tendency to grow in mycelial masses resembling sunbursts, (sulfur granules). These characteristics gave rise to the name actinomyces, meaning "ray fungus," a misnomer resulting from the filamentous nature of the organism. Actinomyces israelii, the most common species in human infection, was first isolated by Israel in 1891, and is the most prone to formation of the characteristic sulfur granules. These small yellow granules can often be grossly visible in the purulent material draining from the sinus tracts which are so typical of chronic infection with these organisms. They are composed of masses of organisms, cemented with host calcium phosphate. Nocardia spp. can also form these structures, but usually do so only in the context of mycetoma, and not in tissue infections. These organisms are normal oral flora, and are routinely seen in the form of sulfur granules in resected tonsil specimens. They are very slow-growing, ultimately forming small, white, opaque, lobulated ("molar tooth") colonies.

Actinomycosis is often characterized by co-infection with "associates," as in this case. They are typically gram negative rods, such as Haemophilus (Actinobacillus) actinomycetemcomitans, other Haemophilus, Fusobacteria, or others. Haemophilus (Actinobacillus) actinomycetemcomitans is endogenous oral flora in humans, and is clinically most often isolated from sites of actinomycosis, resulting in its name. It is, however, also isolated as sole organism in some infections, predominantly wound infections and endocarditis, where it represents one of the so-called HACEK organisms. These are very slow growing, and require and enriched CO2 atmosphere for growth. They are essentially universally susceptible to penicillins, but require very prolonged treatment for eradication. The usual recommendation is a 2-6 week course of IV therapy, followed by an oral course of 6-12 months.

The clinical manifestations of Actinomycosis include craniofacial, thoracic, disseminated, abdominal and pelvic, and central nervous system. Thoracic infection is thought to result from aspiration of oral contents, and can occur in immunocompetent individuals. It is unclear what the primary event leading to infection was in this patient. We know that he presented initially with a flank mass which was consistent with infectious panniculitis. The characteristics suggesting this include the predominance of neutrophils, and the mixed septal and lobular nature of the panniculitis. The possible routes of infection include direct spread from thoracic infection, hematogenous spread from disseminated infection, and forgotten external trauma. Given the extensive nature of the pulmonary involvement at the time of his presentation, it is most likely that the route was by undiagnosed thoracic infection.


  1. Patterson, JW, Brown, PC, and Broecker, AH, "Infection-Induced Panniculitis," Jour Cutaneous Pathology, 1989; 16:183-93.
  2. Russo, T, "Agents of Actinomycosis," in Principles and Practice of Infectious Disease, Mandell, GL, Bennett, JE, and Dolin, R, eds; 4th edition, 1995, pp 2280-88.

Contributed by Richard E. Whisnant, MD, N. Paul Ohori, MD and William Pasculle, ScD


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