Recent changes in taxonomy and disease manifestations of the rapidly growing mycobacteria

Rapidly growing mycobacteria are a complex group of environmental organisms that cause human disease. Eight taxonomic groups of pathogens are recognized of which three, the Mycobacterium chelonae-like organism (MCLO) and the two Mycobacterium fortuitum third biovariant groups, have yet to receive names pending DNA-DNA homology studies. Clinical disease due to all eight taxons usually consists of skin or soft tissue infections following trauma. Nosocomial disease has become increasingly important, pseudoepidemics associated with contaminated automated endoscopic washing machines being the most recently described manifestation. The development of DNA fingerprinting technology, especially pulsed-field gel electrophoresis, has improved the possibilities of studying the epidemiology of these infections. Pulmonary disease, primarily due to Mycobacterium abscessus, and disseminated cutaneous disease due to Mycobacterium chelonae, have recently been characterized. Imipenem and the newer macrolide clarithromycin represent important new therapeutic agents active against these species. Other important therapeutic agents include amikacin and the newer quinolones, which have variable degrees of susceptibility within different taxonomic groups, necessitating susceptibility testing.