Setting. Five IS6110 chromosomal insertion sites were characterized in the multidrug resistant Mycobacterium tuberculosis 'W' strain. Objective: To use insertion site probes to study the phylogenetic distribution of IS6110 in the M. tuberculosis genome, Design: A total of 722 M. tuberculosis isolates, previously genotyped using the standard IS6110 Southern blot hybridization methodology, were re-hybridized with the Region A insertion site probe and representative strains were further hybridized with the Region B and C probes. Strains were grouped on the basis of having IS6110 insertions in these different regions and their relatedness was further compared by sequencing the IS6110 insertion sites. Results. The insertion site probes revealed that the collection of Chinese isolates previously grouped as the Beijing strain family shared IS6110 insertions in common with the W and other genotypic group 1 strains. Unexpectedly, we found that IS6110 integrated at least 10 independent times between the dnaA and dnaN genes encoding deoxyribonucleic acid replication proteins. Conclusions: IS6110 insertion site mapping is able to identify genetic relatedness among a collection of M. tuberculosis clinical strains representing the breadth of species diversity. The mapping data indicate that IS6110 insertion sites are not always random.
Bibliographical noteFunding Information:
This research was supported by Public Health Service Grants Al-37004, AI-41168, and DA-09238 to JMM and R29AI34436 to NDC.