We conducted a 10-year retrospective evaluation of the epidemiology and identification of Nocardia isolates submitted to the Centers for Disease Control and Prevention for antimicrobial susceptibility testing. The species most commonly identified were N. nova (28%), N. brasiliensis (14%), and N. farcinica (14%). Of 765 isolates submitted, 61% were resistant to sulfamethoxazole and 42% were resistant to trimethoprim-sulfamethoxazole.

Four nocardioform bacteria were isolated from clinical respiratory sources (W7467, W7811, W8061T and W9013) in the United States. Macroscopic examination showed scant aerial hyphae and beige-red substrate hyphae. They showed chemotaxonomic markers that were consistent with the classification of Nocardia: i.e., meso-diaminopimelic acid; arabinose and galactose as diagnostic sugars; the phospholipids diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannosides; a menaquinone with a omega-cyclic isoprene side chain MK-8(H4cycl.); a fatty acid pattern composed of unbranched saturated and monounsaturated fatty acids with considerable amount of tuberculostearic acid; and mycolic acids comprising 52 to 62 carbon atoms with three principal mycolic acids which were mono- and polyunsaturated showing a chain length of C54, C56 and C58. 16S rRNA gene sequence data and phenotypic characters showed they were most closely related to Nocardia aobensis (DSM 44805T ). The G+C content was 68.3 mol %. Analysis of a 1,245-bp fragment of gyrB gene showed a clade separate from N. aobensis and was supported by the DNA relatedness of 67 % of W8061T to N. aobensis. These data indicated that the novel isolates represent a new species within the genus Nocardia, for which the name Nocardia mikamii sp. nov. is proposed, with W8061T (DSM 45174T = JCM 15508T) designated as the type strain.