MOLECULAR PHYLOGENY OF THE MYCOBACTERIUM-AVIUM COMPLEX DEMONSTRATES CLINICALLY MEANINGFUL DIVISIONS

Phylogenetic analysis of nucleotide sequence data is widely used for v iral epidemiology. To explore its use in bacterial strain differentiat ion, the variable 16S-23S rDNA internal transcribed spacer (ITS) in 24 clinical isolates originally identified as Mycobacterium avium comple x (MAC) was sequenced. Three isolates had an identical sequence that d iffered greatly from the rest. They belonged to the recently described Mycobacterium celatum. The 21 MAC clinical isolates gave 6 ITS sequen ces, each defining a sequevar. Thirteen isolates from 11 AIDS patients with disseminated MAC disease belonged to 2 sequevars, which differed in ITS sequence by 1 nucleotide. In contrast, 7 pulmonary-source MAC isolates were genetically more diverse. They belonged to 4 sequevars, which differed from each other by 6-20 nucleotides and from the dissem inated disease-associated sequevars by at least 12 nucleotides. The si ngle urine MAC isolate had the same sequence as 1 of the pulmonary iso lates. Because the disseminated disease-associated MAC strains were di stinct by ITS sequence analysis, it should be possible to develop a mo lecular assay to detect them directly in clinical specimens or in envi ronmental samples. Molecular phylogeny at the strain level may be wide ly useful in studies of bacterial epidemiology and virulence.