Nocardia

Nocardia is a genus of weakly staining Gram-positive, catalase-positive, rod-shaped bacteria. It forms partially acid-fast beaded branching filaments (acting as fungi, but being truly bacteria). It contains a total of 85 species. Some species are nonpathogenic, while others are responsible for nocardiosis.Nocardia species are found worldwide in soil rich in organic matter. In addition, they are oral microflora found in healthy gingiva, as well as periodontal pockets. Most Nocardia infections are acquired by inhalation of the bacteria or through traumatic introduction.

Culture and staining

Nocardia colonies have a variable appearance, but most species appear to have aerial hyphae when viewed with a dissecting microscope, particularly when they have been grown on nutritionally limiting media. Nocardia grow slowly on nonselective culture media, and are strict aerobes with the ability to grow in a wide temperature range. Some species are partially acid fast (meaning a less concentrated solution of sulfuric or hydrochloric acid should be used during the staining procedure) due to the presence of intermediate-length mycolic acids in their cell wall. Majority of strains possess the cord factor (trehalose 6-6' dimycolate), an important virulence factor.