Epidemiology of infection by nontuberculous mycobacteria. VI. Identification and use of epidemiologic markers for studies of Mycobacterium avium, M. intracellulare, and M. scrofulaceum.

A comparison of clinical and environmental (e.g., soil, dust, water, and aerosol) isolates of the Mycobacterium avium-intracellulare and M. scrofulaceum (MAIS) group has been made. The frequency of M. avium-intracellulare clinical isolates able to grow without OADC enrichment, able to grow at 43 degrees C, or express resistance to streptomycin or cadmium was significantly higher than those among environmental isolates. Only the frequency of clinical M. scrofulaceum isolates able to grow at 43 degrees C and without OADC enrichment was significantly higher than that of environmental isolates. Because of the high frequency of clinical M. avium-intracellulare isolates able to grow without OADC, grow at 43 degrees C, and resistant to streptomycin, these 3 characteristics are suggested for use as epidemiologic markers for MAIS. There were no significant differences between clinical M. avium-intracellulare isolates from 3 widely separated geographic regions. Among M. avium-intracellulare environmental isolates, only those collected in droplets above bodies of water (i.e., aerosols) shared those characteristics unique to clinical MAIS. That observation suggests that these aerosols are a likely source of human MAIS infection. The ability of isolates to grow at 43 degrees C and without OADC enrichment was highly correlated. Gentamicin-, streptomycin-, and D-cycloserine-resistances were also frequently found together. Isolates carrying plasmids and either able to grow at 43 degrees C, without OADC enrichment, or mercury-resistant were found more frequently than expected as well. This suggests their genetic determinants are plasmid-encoded.