Use of different molecular typing techniques for bacteriological follow-up in a clinical trial with AIDS patients with Mycobacterium avium bacteremia.

One hundred ninety-six Mycobacterium avium isolates from blood samples recovered from 93 AIDS patients for several months were typed by serotyping, by IS1245 restriction fragment length polymorphism (RFLP) analysis and in some cases RFLP analysis with plasmids pVT2 and pLR7 as probes, and by pulsed-field gel electrophoresis (PFGE). PCR typing of single colonies was also used to detect polyclonal infections. Strains belonged mainly to serotypes 1, 4, and 8. pVT2- and pLR7-related plasmids were detected in strains from 49% of the patients. The IS1245 RFLP and PFGE analyses showed a 96.8% diversity of the M. avium strains from the 93 patients. The vast majority (95.2%) of infections were monoclonal, indicating that recent infection is unlikely, even at an advanced stage of AIDS. For one patient, sequential isolates gave divergent patterns of sensitivity and resistance to clarithromycin, but all were identified as the initial clone. RFLP analysis and PCR typing of single colonies allowed for the detection of three polyclonal infections during the bacteriological follow-up. Among strains from patients whose samples were positive by culture after treatment for 2 to 15 months, 97.4% were the same as the initial strain. In conclusion, relapses and failures were mostly due to the initial strain. These relapses and failures resulted either from the selection of resistant mutants or the reappearance of sensitive strains, suggesting the persistence of nonsterilized tissue reservoirs.