Actinomycosis Workup

Updated: Nov 03, 2022
  • Author: Jason F Okulicz, MD, FACP, FIDSA; Chief Editor: Michael Stuart Bronze, MD  more...
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Laboratory Studies

CBC count

Anemia and mild leukocytosis are common.

Erythrocyte sedimentation rate and C-reactive protein

Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels are often elevated.


Chemistry results usually are normal, with the exception of a frequently elevated alkaline phosphatase level in hepatic actinomycosis.

Organism cultures

Because actinomycosis is difficult to diagnose based on the typical clinical features, direct identification and/or isolation of the infecting organism from a clinical specimen or from sulfur granules is necessary for definitive diagnosis in most cases.

Acceptable specimen material is obtained from draining sinuses, deep needle aspirate, or biopsy specimens; swabs, sputum, and urine specimens are unacceptable or inappropriate.

Prompt transport of the specimens to the microbiology laboratory is necessary for optimal isolation of actinomycetes, preferably in an anaerobic transport device.

A Gram-stained smear of the specimen may demonstrate the presence of beaded, branched, gram-positive filamentous rods, suggesting the diagnosis of actinomycosis.

Cultures should be placed immediately under anaerobic conditions and incubated for 48 hours or longer; the isolation and definitive identification of actinomycetes may require 2-3 weeks.

Nucleic acid probes and polymerase chain reaction (PCR) methods are being developed for more rapid and more accurate identification.

Antimicrobial susceptibility testing is not indicated in the management of actinomycosis, partly because of their predictable antibiogram.

Sulfur granules

The preliminary diagnosis of actinomycosis also can be made by examining sulfur granules. Granules should be crushed between 2 slides, stained with 1% methylene-blue solution, and examined microscopically for features characteristic of actinomycetes.

Serologic diagnosis

Current serologic tests have no role in diagnosing actinomycosis.

Papanicolaou test

The relationship between a Papanicolaou test that is positive for actinomycetelike organisms and the eventual development of pelvic actinomycosis is unclear.

The prevalence of smears positive for Actinomyces organisms in women who use IUCDs is approximately 7%. [9]

Because of the lack of sensitivity and specificity and low positive predictive value, the prognostic significance of detecting Actinomyces organisms is minimal in the absence of concomitant symptoms. [9]


Imaging Studies

Chest radiography

A chest radiograph may reveal a poorly defined mass or pneumonitis or cavitary lesion, with or without pleural involvement. Hilar adenopathy is uncommon.

The presence of a masslike lesion that extends across fissures or pleura, invades into the adjacent chest wall or thoracic vertebrae, or causes local destruction of the ribs or sternum suggests thoracic actinomycosis.

CT scanning

CT scanning (irrespective of the anatomic area of involvement) usually reveals an infiltrative mass with focal areas of decreased attenuation that enhance with contrast. This infiltrative mass tends to invade surrounding tissues. Surrounding lymphadenopathy is uncommon.



CT scan or ultrasound-guided fine-needle aspiration and/or biopsy have been used successfully to obtain clinical material for diagnosis of actinomycosis.

Surgery (eg, thoracotomy with open lung biopsy, exploratory laparotomy) may be required for diagnostic purposes.


Histologic Findings

Actinomycosis is characterized by mixed suppurative and granulomatous inflammatory reactions, connective-tissue proliferation, and the presence of sulfur granules. The sulfur granules are nearly pathognomonic for actinomycosis, although similar findings have been reported with infections caused by Nocardia brasiliensis, Streptomyces madurae, and Staphylococcus aureus presenting as botryomycosis. The granules are approximately 0.1-1 mm in diameter and may be seen with the naked eye as yellowish particles.

Microscopically, the granules manifest a cauliflowerlike shape at low magnification; at higher magnification (X100), when the particle has been pressed between slide and cover slip, a clump of filamentous actinomycete microcolonies surrounded by polymorphonuclear neutrophils (PMNs) can be observed. Gram stain renders these microcolonies visible as gram-positive, intertwined branching filaments, with radially arranged, peripheral hyphae. Coexisting with them are the companion bacteria, which are gram-positive and gram-negative cocci and rods. The images below are representative photomicrographs.

Actinomycosis in the endometrial tissue, low-power Actinomycosis in the endometrial tissue, low-power view. Image courtesy of Paul Gibbs, MD.
Actinomycosis in the endometrial tissue, high-powe Actinomycosis in the endometrial tissue, high-power view. Image courtesy of Paul Gibbs, MD.