IS6110-based global phylogeny of Mycobacterium tuberculosis

IS6110, a Mycobacterium tuberculosis complex species-specific insertion element, is targeted primarily for DNA fingerprinting of M. tuberculosis strains. The number and chromosomal positions of copies of this element have been found to be highly variable between unrelated strains and have been exploited for molecular epidemiological purpose but the utility of IS6110 as an informative marker of strain phylogeny has yet to be demonstrated. In the current study, a recently proposed IS6110-targetting PCR based typing methodology, fluorescent amplified fragment length polymorphism (fAFLP) was applied to a global panel of 166 of the clinically more predominant 'modern' strains characterised by spoligotype and, where available, Variable Number Tandem Repeat (VNTR) to identify potentially evolutionarily informative common fragments that could define strains as belonging to established genetic lineages. These common fragments are hereby proposed to be ancestral insertion sites present in common ancestors of these strains rather than preferential insertion sites or 'hot spots'. Results indicate that the exact same spoligotype and VNTR-defined lineages are reflected in the fragment patterns but with greater resolution and are able to clearly define the very distinct Haarlem, LAM, X and also the currently ill-defined T and S and lineages and spoligotypes designated as U, or unknown, without ambiguity. The biogeographical patterns generated reflect the migration of mankind across the globe and indicate that only four successful clones (or individual bacteria) gave rise to virtually all of the tuberculosis in Europe and the Americas. Potential lies in the application of the data to determine IS6110 evolutionary events that have occurred during the evolution of these lineages.