Editorial ENVIRONMENTAL MYCOBACTERIA AND HUMAN DISEASE in the latter part of the last century, the causative organisms of leprosy and tuberculosis were described, respectively, by Armauer Hansen in 1874 and Robert Koch in 1882. These bacteria were distinguished from all others known at that time by a characteristic acid-fast staining property by Paul Ehrlich in 1883. In 1898, when the generic name Mycobacterium was introduced, no other acid-fast bacillus had been formally described and named

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... from that time onwards many such organisms were isolated from environmental sources and from diseased mammals, birds and cold-blooded animals. A few were also isolated from patients, but their role as human pathogens was not seriously considered until the middle of this century when two new mycobacterial skin diseases, swimming pool granuloma I and M. ulcerans infection,2 later termed Buruli ulcer, were described and when Runyon published his classical description of the four groups of mycobacteria causing pulmonary disease.3 Many unsatisfactory collective names including 'atypical', 'anonymous', 'tubercu loid' and 'MOTT (mycobacteria other than typical tubercle) bacilli' have been given to these mycobacteria but when it became apparent that these species were not primarily pathogenic but widely distributed in nature, the name 'environmental mycobacteria' (EM) was generally adopted. At present there are about 60 known mycobacterial species: 41 are included in the Approved Lists of Bacterial Names4 published in 1980 and the others have been described subsequently.5 Cultivable mycobacteria are divisible into two main groups: the slow and rapid growers, which, by antigenic analysis and DNA homology, appear to belong to two quite distinct subgenera. The ecology of the environmental mycobacteria It is not generally appreciated just how common the EM are in nature. Sphagnum marshes contain very large numbers6 and they are also readily isolated from mud, compost, wet soil, surface water, rivers and estuaries.7 Some species colonize piped water supplies and have been isolated from taps and showerheads. There is also evidence that mycobacteria are washed into estuaries, taken up into aerosols generated by breaking waves and wafted inland by sea breezes and thereby sensitize people who inhale them.8 Some species or strains are more hydrophobic than others and thus more readily enter 0305-7518/91/062353+09 $01.00 © Lepra