There are no data so far that show IS6110 restriction fragment length polymorphism (RFLP) patterns of individually separated tuberculosis bacilli from clinical isolates, and their alterations during follow-up surveys. We picked 20–60 tuberculosis clones from clinical isolates under anti-tuberculosis medication, and individually analysed their DNA fingerprinting patterns using IS6110 RFLP as well as spoligotyping as a second typing.

The study using cloned bacilli of Mycobacterium tuberculosis showed that clinical isolates contained several clones with different DNA fingerprints and that their band patterns altered weakly but distinctly during follow-up surveys. However, there was no significant difference in the fingerprinting patterns when clinical isolates were to RFLP without separating to subjected/individual colonies.

In view of the IS6110 RFLP of individually separated tuberculosis bacilli, we have now speculated several possibilities: (1) that clones with different DNA fingerprints exist in clinical isolates; (2) that IS6110 RFLP patterns of the materials depend on the population of the original clone and the variants having DNA fingerprints different from the original pattern; and (3) that their band patterns are influenced not only by the stability of the original germ having its own fingerprint, but also by the fragility of the new clones.