Nontuberculous Mycobacteria - Taxonomy

Taxonomy

In 1959, botanist Ernest Runyon put these human disease-associated bacteria into four groups (Runyon classification):

• Photochromogens, which develop pigments in or after being exposed to light. Examples include M. kansasii, M. simiae and M. marinum.
• Scotochromogens, which become pigmented in darkness. Examples include M. scrofulaceum and M. szulgai.
• Non-chromogens, which includes a group of prevalent opportunistic pathogens called M. avium complex (MAC). Other examples are M. ulcerans, M. xenopi, M. malmoense, M. terrae, M. haemophilum and M. genavense.
• Rapid growers include four well recognized pathogenic rapidly growing non-chromogenic species: M. chelonae, M. abscessus, M. fortuitum and M. peregrinum. Other examples cause disease rarely, such as M. smegmatis and M. flavescens.

The number of identified and cataloged NTM species has been increasing rapidly, from about 50 in 1997 to over 125 by January 2007. The surge is mainly due to improved isolation and identification technique.

However, even with these new techniques, the Runyon classification is still sometimes used to organize the mycobacteria into categories.