Plasmid analysis of Mycobacterium avium-intracellulare (MAI) isolated in the United Kingdom from patients with and without AIDS.

One hundred and forty-seven isolates (128 strains) of Mycobacterium avium-intracellulare (MAI) were screened by agarose gel electrophoresis for the presence of plasmids. Plasmids were characterised according to size and by Southern hybridisation analysis of intact and restriction endonuclease-digested DNA. Two cloned MAI plasmids, pLR7 and pLR20, were used as probes. There was no significant difference in the rate of plasmid carriage in MAI strains isolated from patients with the acquired immuno-deficiency syndrome (AIDS) and from non-AIDS patients in the UK, but a higher rate of plasmid carriage was observed in a panel of American strains from AIDS patients. Plasmids were grouped into two broad categories: small (mostly 14-30 kb) and large (greater than 150 kb). Southern blot analysis identified two distinct groups of small plasmids, the majority of which showed homology with pLR7. Plasmids from this group were significantly more common in strains of serotypes 4 and 8 which are particularly associated with AIDS.