Analysis of plasmids in Mycobacterium avium-intracellulare isolates from persons with acquired immunodeficiency syndrome.

Twenty-six strains of the Mycobacterium avium complex isolated from persons with AIDS were examined for plasmid content. The strains were of serotypes 4, 8, 4/6, and 4/8. Plasmid content was determined by agarose gel electrophoresis. All 26 strains carried small plasmids (9 to 15 Mdal), with 11 strains carrying 1 small plasmid and 15 carrying 2. Ten strains also carried large plasmids (greater than 100 Mdal), and 1 strain carried a 60 Mdal plasmid. We have reported molecular cloning of plasmid pLR7, a small plasmid derived from a serotype 4 strain. Cloned segments of pLR7 were used as hybridization probes to detect homologous plasmids in the AIDS-associated strains. Each of the 26 strains carried a plasmid closely related to pLR7. Considerable heterogeneity of size and restriction sites was observed. The finding of plasmids in all strains raises the possibility that they may play a role in virulence. The plasmids will serve as a useful marker for epidemiology and might be useful as probes for detecting M. avium-intracellulare in clinical material.