MYCOBACTERIUM-AVIUM BACILLI GROW SAPROZOICALLY IN COCULTURE WITH ACANTHAMOEBA-POLYPHAGA AND SURVIVE WITHIN CYST WALLS

Protozoans are gaining recognition as environmental hosts for a variet y of waterborne pathogens. We compared the growth of Mycobacterium avi um, a human pathogen associated with domestic water supplies, in cocul ture with the free-living amaoeba Acanthamoeba polyphaga with the grow th of M. avium when it was separated from amoebae by a 0.1-mu m-pore-s ize polycarbonate membrane tin a parachamber), Although viable mycobac teria were observed within amoebal vacuoles, there was no significant difference between bacterial growth in coculture and bacterial growth in the parachamber. This suggests that M. avium is able to grow saproz oically on products secreted by the amoebae. in contrast, Legionella p neumophila, a well-studied intracellular parasite of amoebae, multipli ed only in coculture. A comparison of amoebae infected with L. pneumop hila and amoebae infected with M. avium by electron microscopy demonst rated that there were striking differences in the locations of the bac teria within amoeba cysts. While L. pneumophila resided within the cys ts, M. avium was found within the outer walls of the double-availed cy sts of A. polyphaga. These locations may provide a reservoir for the b acteria when environmental conditions become unfavorable.