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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, which are 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. can cause primary cutaneous disease, ranging from cellulitis to paronychia to abscesses, with the most striking presentation being a lymphocutaneous, sporotrichoid syndrome; cutaneous nocardiosis as a consequence of hematogenous dissemination from a pulmonary source is also seen, but it is characteristically of a state of immunosuppression. In addition, other aerobic environmental species of Nocardia and Actinomyces will cause 1 of the 2 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 158-1). Practicing dermatologists should be aware of the various morphologic variants of these diseases and the measures that should be taken to ensure the appropriate culturing techniques required for isolation.

Table 158-1Diagnostic Approach to Diseases That Produce Grains



  • Worldwide distribution, relatively uncommon.

  • Actinomyces are part of normal upper respiratory, intestinal, and genitourinary flora.

  • Actinomyces israelii is the most common causative agent, usually as part of a polymicrobial infection, mixed with anaerobes and Gram-positive cocci.

  • Classical presentation is a chronic, localized, infiltrative, bulging process with abscess fistula formation and draining sinuses.

  • Most common location is cervicofacial (related to dental pathology), followed by chest wall, abdominal, and pelvic involvement.

  • Pathologic findings include a ...

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