Updated Review on Nocardia Species: 2006-2021

Abstract

This review serves as an update to the previous Nocardia review by Brown-Elliott et al. published in 2006 (B. A. Brown-Elliott, J. M. Brown, P. S. Conville, and R. J. Wallace. Jr., Clin Microbiol Rev 19:259-282, 2006, https://doi.org/10.1128/CMR.19.2.259-282.2006). Included is a discussion on the taxonomic expansion of the genus, current identification methods, and the impact of new technology (including matrix-assisted laser desorption ionization-time of flight [MALDI-TOF] and whole genome sequencing) on diagnosis and treatment. Clinical manifestations, the epidemiology, and geographic distribution are briefly discussed. An additional section on actinomycotic mycetoma is added to address this often-neglected disease.

Keywords: Nocardia; aerobic actinomycetes; mycetoma; nocardiosis.

FIG 1

(A) Nocardial brain abscess. Routine hematoxylin & eosin (H&E) stain shows necrosis, karyorrhectic debris, and neutrophilic infiltrate in the abscess. Original magnifications: X200. (B) Nocardial lung infection with granulomatous inflammation. H&E stain shows a granuloma with central necrosis, lymphohistiocytic infiltrate at the periphery, and rare multinucleated cells (arrow). Original magnifications: X100. (C) Nocardial skin infection. H&E stain shows a zone of mixed inflammatory infiltrate (arrows) and large area of abscess formation (arrowheads) in the dermis. Original magnifications: X50. (D) Nocardial skin infection with granulomatous inflammation. H&E stain shows a granuloma (arrow) with central necrosis and lymphohistiocytic infiltrate at the periphery, as well as scattered multinucleated cells in adjacent area (arrowheads). Original magnifications: X100. (E) Nocardial skin infection. H&E stain shows dense aggregated granules (grains) with a peripheral radial deposition of intensely eosinophilic material (arrows) – a Splendore-Hoeppli phenomenon. Original magnifications: X100. (F) Gram stain showing scattered Gram-positive and gram-variable nocardial organisms in the abscess. Original magnifications: X400. (G) Grocott methenamine silver (GMS) stain showing clusters of filamentous nocardial organisms in the abscess. Original magnifications: X400. (H) Steiner silver stain showing clusters of filamentous nocardial organisms in the abscess. Original magnifications: X400.