EPIDEMIOLOGY OF INFECTION WITH ATYPICAL MYCOBACTERIA

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Previous studies have demonstrated a good correlation between the incidence of persons reacting strongly to antigens (PPD-B, PPD-G) prepared from atypical (nontuberculous) mycobacteria and the geographic distribution of these strains in natural waters. Because soil contains many more mycobacteria of the Mycobacterium avium, M. intracellulare and M. scrofulaceum (MAIS) group than water, MAIS in water and air may originate from soil. One objective of this proposal will be to test that hypothesis. Though MAIS strains isolated from the environment predominate in the southeastern United States, where the greatest frequency of reactors to PPD-B and PPD-G reside and serotypes encountered in human isolates are found in environmental strains, we propose to identify a large number of epidemiological markers of MAIS strains (e.g. antibiotic, dye, metal, and detergent sensitivity, plasmid DNA content and synthesis of extracellular enzymes) in order to prove more convincingly that human infection is due to MAIS strains in the environment. Heavy metal resistance has been shown to have a unique geographic distribution among environmental isolates, which suggests that testing human isolates recovered from the same and different regions will test the hypothesis. In addition to studying the geographic incidence of MAIS strains we propose to investigate the interaction and behavior of MAIS organisms in soil. Approximately 5% of cells added to soil can be recovered by aqueous extraction, suggesting there are strong interactions (hydrophobic?) and that environmental surveys only represent 5% of the MAIS organisms. The fact that water can extract some MAIS organisms indicates that rainfall is expected to lead to increases in water-borne MAIS. Our continuing studies of MAIS physiological ecology have demonstrated that salinity and temperature are determinants of MAIS geographic distribution and the fact that pigmented, catalase-positive strains predominate in the southeast indicates that light and toxic photoproducts and superoxide- and peroxide-consuming enzymes may be involved in MAIS ecology. Finally, because of the high numbers of MAIS in soil, their growth and interaction (adsorption and elution) will be studied with respect to cell surface characteristics, serotype and colonial phase.