Mapping of IS 6110 Insertion Sites in Two Epidemic Strains of Mycobacterium tuberculosis

Abstract

A widely distributed strain designated 210 was identified in a study of the diversity of Mycobacterium tuberculosis DNA fingerprints from three geographically 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 that of isolates from other clusters or nonclustered isolates. The purpose of this study was to identify the sites of IS6110 insertions in strain 210 and compare these to IS6110 insertion sites in strain W. Our hypothesis is that an IS6110 insertion site(s) could possibly be responsible for a strain's increased capacity for transmission and/or replication. In this report, the insertion sites in strains 210 and W are described and referenced to their location in the M. tuberculosis H37Rv genome sequence. The W and 210 strains have 17 identical sites of IS6110 insertion and additional sequence not found in H37Rv but present in other clinical isolates. The IS6110insertion site in the 36-bp direct repeat (DR) region of strains 210 and W has 15 spacers in the left flanking region. The DR region on the right side of IS6110 has been deleted. Five sites of insertion in strain 210 not found in strain W are described, as well as two unique sites in strain W. One copy of IS6110 was found to reside 55 bp in the ctpD gene. This gene is expressed, indicating that IS6110 can provide a promoter sequence for the transcription of genes.

Unsuspected and extensive transmission of a drug-susceptible Mycobacterium tuberculosisstrain

“…However, the percentage of infected children was surprisingly low in view of the dissemination of this strain among the total population in Zaragoza. Like strains involved in other outbreaks, the MTZ strain might have unique characteristics for virulence and/or transmissibility [ 36 - 39 ]. The transmission of tuberculosis may have been due to the increased virulence of the strain rather than to environmental factors or patient characteristics.…”

Evidence for a rapid rate of molecular evolution at the hypervariable and immunogenic Mycobacterium tuberculosis PPE38 gene region

“…Also of note is the finding that of all IS 6110 integrations that were found to disrupt the 4 PPE genes analysed here, all occurred in their 5' (conserved N-terminal) regions. Apart from the obvious negative functional effects of gene deletion and disruption, IS 6110 can also function as a mobile promoter and upregulate genes located downstream of its integration site [ 43 - 45 ]. Three of our clinical isolates revealed IS 6110 integrations upstream of genes and an investigation into the transcriptional effects could be of interest.…”

Towards a quantitative perception of human-microbial co-evolution

“…DR locus consists of minisatellite alternating exact direct repeats and variable spacers. In the Bj genotype, most of the DR units were deleted during evolution, perhaps by a single event mediated by IS6110 recombination (17). The Bj strains may be further discriminated by minisatellite VNTR (variable number of tandem repeats) loci (2, 18, and references therein).…”