RT Book, Section A1 Bravo, Francisco G. A1 Arenas, Roberto A1 Sigall, Daniel Asz A2 Kang, Sewon A2 Amagai, Masayuki A2 Bruckner, Anna L. A2 Enk, Alexander H. A2 Margolis, David J. A2 McMichael, Amy J. A2 Orringer, Jeffrey S. SR Print(0) ID 1161375969 T1 Actinomycosis, Nocardiosis, and Actinomycetoma T2 Fitzpatrick's Dermatology, 9e YR 2019 FD 2019 PB McGraw-Hill Education PP New York, NY SN 9780071837798 LK dermatology.mhmedical.com/content.aspx?aid=1161375969 RD 2024/10/11 AB 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.