Actinomycosis

Published on 18/03/2015 by admin

Filed under Dermatology

Last modified 22/04/2025

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Actinomycosis

Jonathan E. Blume and Daniel Caplivski

Evidence Levels:  A Double-blind study  B Clinical trial ≥ 20 subjects  C Clinical trial < 20 subjects  D Series ≥ 5 subjects  E Anecdotal case reports

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Actinomycosis is often an indolent infection that may be difficult to recognize initially. It is caused by an anaerobic Gram positive rod that is a normal human commensal. Infections caused by Actinomyces spp. are usually the result of introduction of the bacteria into a normally sterile space from the oropharynx, gastrointestinal tract or vaginal tract. The organism may be difficult to recover in the microbiology laboratory because it grows slowly and is ideally cultured under anaerobic conditions. Microscopically, it has a similar appearance to Nocardia spp.; however, it does not retain the modified acid fast stain and the colonies may have a molar tooth appearance. Infections of the cervical region are typified by the slow induration of the skin at the angle of the jaw that progresses over several weeks or months. A mass may be palpable and, due to the slow progression and absence of systemic inflammatory symptoms, the infection can often be confused with other conditions such as malignancies. Patients may notice the discharge of small yellow grains known as ‘sulfur granules.’ These are macroscopic colonies of the organism that may be cultured for confirmation, but their absence should not exclude the diagnosis from consideration.

Management strategy

Actinomyces spp. are universally susceptible to penicillin. The severity of the illness will dictate whether the patient requires intravenous or oral formulations of the antibiotic, but the general principle is that prolonged treatments for 6 months or more are often required for cure. In patients who are penicillin allergic, the tetracycline class of antibiotics is a useful substitute. Surgical removal of the abscess may also be required in order to ensure complete resolution. Treatment failures are rare, but may be due to co-infecting organisms from the oropharynx. In order to treat these organisms, the combination of a β-lactam antibiotic with a β-lactamase inhibitor may be sufficient. Carbapenems such as imipenem, meropenem, or ertapenem are also effective.

Specific investigations

Diagnostic methods for human actinomycosis.

Holmberg K. Microbiol Sci 1987; 4: 72–8.

An excellent review of the diagnosis of actinomycosis.

The most accurate way to diagnose actinomycosis is via culture – usually a difficult task, which requires thioglycolate or brain–heart-enriched agar at 37°C under anaerobic or microaerophilic conditions. ‘Molar-tooth’ and ‘breadcrumb’ colonies may take up to 3 weeks to grow. Unfortunately, definitive identification cannot be based on colony morphology and requires the measurement of physiological and biochemical characteristics (e.g., sensitivity to oxygen, presence of preformed enzymes).

Because cultures of Actinomyces spp. are often unsuccessful, observation of ‘sulfur granules’ on a peripheral smear or histology often helps make the diagnosis. The granules are bacterial colonies which on hematoxylin and eosin staining have a basophilic central area surrounded by a zone of eosinophilic ‘clubs’. Other typical histologic findings include extensive fibrosis, chronic granulation tissue, sinus tracts, and scattered microabscesses.

Immunofluorescent staining of Actinomyces spp. is available and can be used on clinical material, granules, and formalin-fixed tissues. The direct immunoperoxidase technique can specifically show Actinomyces spp. in formalin-fixed sections via light microscopy. These techniques, as well as gene sequencing (see below), are promising diagnostic modalities given the difficulty of culture and histologic identification.

First-line therapies

imagePenicillin C

Second-line therapies

imageAmoxicillin C
imageCeftriaxone D
imageClindamycin C
imageDoxycycline D
imageErythromycin D
imageImipenem C
imageMinocycline C
imageTetracycline D

Third-line therapies

imageCiprofloxacin E
imageLevofloxacin E
imageRifampin E
imageHyperbaric oxygen E

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