[Mycobacteria in the environment]

Mycobacteria typically are free-living environmental saprophytes and strict pathogens such as M. tuberculosis and M. leprae, which do not proliferate in the inanimate environment form rare exceptions within the genus Mycobacterium. Many free-living mycobacteria such as M. avium and M. kansasii have been described as potential human pathogens and there is evidence that they are usually transmitted by inhalation, inoculation and ingestion from environmental sources. Soil, bogs, surface water, ground water and sea water have been described as natural habitats of environmental mycobacteria. In addition, artificial habitats such as tap water and sewage sludge are colonized by a considerable spectrum of mycobacterial species. Aquatic mycobacteria tend to colonize biofilms at air-water and solid-water interfaces and the latter seem to be an important proliferation site in oligotrophic habitats. Outside the host tissue M. chelonae ssp. abscessus, M. kansasii, M. simiae, and M. xenopi have so far almost exclusively been isolated from artificial oligotrophic aquatic habitats, i.e. tap water and drinking water; their natural reservoir is unknown. Some species have not yet been isolated from the environment although epidemiological data suggest that infections caused by these organisms are acquired from environmental sources.