Atypical mycobacteria

The nontuberculous mycobacteria are species different from Mycobacterium tuberculosis. In the past these organisms were referred to as “atypical” (as they were thought to be unusual M. tuberculosis strains), as “anonymous”, as “tuberculoid”, or as “opportunistic”, but actually they are widely known as environmental mycobacteria because their peculiar ability to exist in the environment. Their existence has been known since the nineteenth century, but their role as human pathogens was not seriously considered until the middle of the twentieth century when a new mycobacterial skin disease called swimming pool or fish tank granulomas, due to Mycobacterium marinum, was described by Linell and Norden and Runyon published his classification of the mycobacteria. Environmental mycobacteria (Table 6.1) are acid-fast mycobacteria, have a wide distribution, and can be found in up to 90% of biofilms (the slim layer present at the water-solid interfaces) taken from piped water systems. They are extremely hardy and thrive in even the most hostile environments; some species such as the Mycobacterium chelonae or Mycobacterium abscessus group resist the activity of disinfectants and biocides such as organomercurials, chlorine, and alkaline gluteraldehyde. Pseudo-outbreaks of mycobacteriosis related to contaminated surgical instruments have been described all over the world. Mycobacteria, therefore, can easily affect the skin; in some cases, especially in immunosuppressed patients, they are able to spread toward the pulmonary or lymphoglandular system and even reproduce a systemic illness.