It is difficult to distinguish between clinically significant slowly-growing, non-pigmented mycobacteria, notably to separate M. avium and M. intracellulare from one another and from M. scrofulaceum strains. The purpose of this study was to evaluate the extent to which 16S rRNA sequencing could be used to highlight the taxonomic relationships of the mycobacterial strains, which are difficult to separate using conventional microbiologic methods. Almost the complete sequences of the 16S rRNA of several M. avium-intracellulare complex strains were determined following the isolation and direct sequencing of the amplified genes. The sequences were aligned with those of previously studied mycobacteria, and phylogenetic trees inferred by using the Fitch-Magoliash, neighbour-joining and maximum parsimony methods. It is evident from the result of the current study that the nucleotide signature regions of 16S rRNA provide valuable information for the differentiation of M.avium-intracellulare complex strains
