SUMMARY: A new genus has been proposed for slightly acid-fast organisms which occur in sputa of patients with pulmonary disease and in soil. This genus is considered to contain ‘Mycobacterium’ rhodochrous-like organisms. The genera and are characterized by absence of mycelium and slight or strong acid-fastness. The genus shows characters intermediate between the genera and It is distinguished from rapid-growing mycobacteria by its slight acid-fastness (weaker than ), absence of arylsulphatase activity at 2 weeks, ability to utilize sucrose as a sole carbon source and inability to utilize trimethylene diamine as a simultaneous nitrogen and carbon source. The genus is distinguished from nocardias by the absence of mycelium, ability to form acid from mannose, positive nitrate reduction and ability to utilize sucrose as a sole carbon source. It can be isolated from sputa of patients with lung cavities or bronchiectasis and from soil by prior treatment with alkali. The organisms are Gram-positive or variable; slightly acid-fast, that is, stained light pink or light violet by the Ziehl-Neelsen method; mycelium not formed; spores not formed; non-motile; aerobic; catalase-positive; oxidase-negative; acid formed from glucose by oxidation; growth occurs at 28° and 37° but not at 45°; growth at 2 to 3 days forming rough, reddish or pinkish colonies in air; occur as short rods; non-pathogenic for mice, rabbits, guinea pigs and chickens. Type species is


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