Mapping of IS6110 insertion sites in two epidemic strains of Mycobacteriumtuberculosis

A widely distributed strain designated 210 was identified in a study of the diversity of Mycobacterium tuberculosis DNA fingerprints from three geogra phically separate states in the United States. This strain is characterized by a 21-band fingerprint pattern when probed with IS6110, and the pattern is similar to that displayed by strains designated W. Intracellular growth of strain 210 isolates in human macrophages is significantly faster than th at of isolates from other clusters or nonclustered isolates. The purpose of this study was to identify the sites of IS6110 insertions in strain 210 an d compare these to IS6110 insertion sites in strain W. Our hypothesis is th at an IS6110 insertion site(s) could possibly be responsible for a strain's increased capacity for transmission and/or replication. In this report, th e insertion sites in strains 210 and W are described and referenced to thei r location in the M. tuberculosis H37Rv genome sequence. The W and 210 stra ins have 17 identical sites of IS6110 insertion and additional sequence not found in H37Rv but present in other clinical isolates. The IS6110 insertio n site in the 36-bp direct repeat (DR) region of strains 210 and W has 15 s pacers in the left flanking region. The DR region on the right side of IS61 10 has been deleted. Five sites of insertion in strain 210 not found in str ain W are described, as well as two unique sites in strain W. One copy of I S6110 was found to reside 55 bp in the ctpD gene. This gene is expressed, i ndicating that IS6110 can provide a promoter sequence for the transcription of genes.