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Actinomyces and Nocardia are a group of filamentous bacteria belonging to the same class, Actinobacteria, and same order, Actinomycetales. They cause human disease with prominent skin involvement. Microorganisms under this category were wrongly classified as fungi for a long time, because of their tendency to produce branching filaments, mimicking radiating hyphae (from the Greek actino, meaning sun). Their taxonomy is still evolving, resulting in continuous reclassification of different species in old and new families. Anaerobic endogenous Actinomyces, part of our normal respiratory, intestinal, and genitourinary flora, will cause localized suppurative disease with fistula formation that is analogous to the lumpy jaw of cattle. Aerobic environmental Nocardia sp. cause diseases ranging from cellulitis to paronychia to abscesses, with the most striking presentation being a lymphocutaneous, sporotrichoid syndrome. In addition, other aerobic environmental species of Nocardia and Actinomyces will cause one of the two known forms of mycetoma, the actinomycetoma.

The sulfur granule or grain, a clumping of filamentous bacteria seen in infected living tissue, is considered characteristic of the infection by these microorganisms, but is not always present and is also not specific (Table 185-1). Practicing dermatologists should be aware of the various morphologic variants of these diseases, so that measures may be taken to ensure the appropriate culturing techniques required for isolation.

Table 185-1 Infectious Diseases with Production of Grains
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Actinomycosis at a Glance
  • Worldwide distribution, relatively uncommon.
  • Actinomyces are part of normal upper respiratory, intestinal, and genitourinary flora.
  • Actinomyces israelii is the most common causative agent, usually mixed with Gram-positive cocci and anaerobes.
  • Classical presentation is a chronic, localized infiltrative process with abscess fistula formation and draining sinuses.
  • Most common location is cervicofacial (related to dental pathology), followed by abdominal, pelvic, and chest wall involvement.
  • Pathologic findings include a chronic inflammatory infiltrate with granulation tissue or granuloma formation.
  • Grains (sulfur granules) are characteristic but neither invariably present nor pathognomonic.

Epidemiology

Described by Israel in 1878, the disease has a worldwide distribution. It is more commonly seen in males, ages 20–60, ...

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