Nocardia spp. is a Gram-positive aerobic bacillus of the genus Nocardia. The species of the Nocardia genus in the family Nocardiaceae form a homogeneous cluster among the Corynebacteriaceae, a suborder of the Actinomycetales order.
Since its isolation by Edmond Nocard in 1888, there have been various reclassifications of a varied number of species of Nocardia. Currently, the Nocardia genus contains more than 50 species that have been characterized using phenotypic and molecular methods. Brown-Elliot et al. [2**] carried out a review of the clinical and laboratory features of Nocardia spp. based on the current molecular taxonomy.
All of these species, however, have not undergone the same level of analysis and study. Of all the species accepted, approximately one-half have been recognized as pathogens in humans and/or animals. The aerosol route is the main portal of entry into the body, and the lungs are the most common sites of infection. Species that produce pulmonary or disseminated infection (four or more known cases) include Nocardia asteroides, N. abcessus, N. farcinica, N. pseudobrasiliensis, N. transvalensis, N. nova, N. otitisdiscaviarium, N. africana, N. asiatica, N. beijingensis, N. cyriacigeorgica, N. higoensis, N. paucivorans and N. veterana ( Table 1 [2**,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]).
Other modes of entry include ingestion of contaminated food or direct inoculation of the organism as a result of trauma. Human-to-human transmission has not been documented. There have however, been rare reports of clusters of patients infected with identical strains of Nocardia while occupying beds in close proximity to one another in hospital wards. In such cases, nosocomial acquisition is probable.[20,21]
Curr Opin Pulm Med. 2008;14(3):219-227. © 2008 Lippincott Williams & Wilkins
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