DNA probes demonstrate a single highly conserved strain of Mycobacterium avium infecting AIDS patients.

Strains of the Mycobacterium avium intracellulare complex (MAIC) have become important colonisers of patients with acquired immunodeficiency syndrome (AIDS). Restriction fragment length polymorphisms were used to study the DNA from 88 MAIC isolates, including 51 derived from 47 AIDS patients. MAIC isolates from 33 of 45 AIDS patients were identical at the molecular level and distinct from the mycobacteria isolated from the stools of healthy subjects. The study also showed that serotyping correlates poorly with the genetic identity of these organisms. Mycobacterium paratuberculosis, which has been implicated in Crohn's disease, was not identified in any of the cultures studied.