INTERACTION OF MYCOBACTERIUM-AVIUM WITH ENVIRONMENTAL AMEBAS ENHANCESVIRULENCE

Environmental mycobacteria are a common cause of human infections, Rec ently, contaminated domestic water supplies have been suggested as a p otential environmental source of several mycobacterial diseases, Since many of these mycobacterial species replicate best intracellularly, e nvironmental hosts have been sought, In the present study, we examined the interaction of Mycobacterium avium with a potential protozoan hos t, the water-borne amoeba Acanthamoeba castellanii. We found that M. a vium enters and replicates in A. castellanii. In addition, similar to that shown for mycobacteria within macrophages, M. avium inhibits lyso somal fusion and replicates in vacuoles that are tightly juxtaposed to the bacterial surfaces within amoebae. In order to determine whether growth of M. avium in amoebae plays a role in human infections, we tes ted the effects of this growth condition on virulence, We found that g rowth of M. avium in amoebae enhances both entry and intracellular rep lication compared to growth of bacteria in broth, Furthermore, amoeba- grown M. avium was also more virulent in the beige mouse model of infe ction. These data suggest a role for protozoa present in water environ ments as hosts for pathogenic mycobacteria, particularly M. avium.