Figure 1: (A) Schematic presentation of the polymorphism in DR regions of different M. tuberculosis complex strains. Blocks of DVR are missing in one strain when compaired to another. The spacer order remains about the same. (B) Principle of the in vitro amplification of DNA within the DR region of M. tuberculosis complex bacteria. The use of the 2 primers, a and b, for in vitro amplification, will lead to the amplification of any spacer or a stretch of neighbouring spacers and DR's. (C) Spoligotyping result of M. tuberculosis H37Rv, M. bovis BCG P3 and 38 different clinical isolates. A membrane with 43 spacer oligonucleotides was used (vertical lines). The spacer oligonucleotides were derived from the spacers of M. bovis V BCG P3, M. tuberculosis H37Rv.