Journal of Bacteriology, September 2001, p. 5279-5284, Vol. 183, No. 18
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.18.5279-5284.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Public Health Laboratory Services Mycobacteria Reference Unit and Department of Infection, Guy's, King's and St. Thomas' School of Medicine, London,1 Department of Medical Microbiology, University of Aberdeen, Aberdeen,2 and Scottish Mycobacteria Reference Laboratory, The City Hospital, Edinburgh,3 United Kingdom, and Department of Microbiology, Mahidol University, Bangkok, Thailand4
Received 2 August 2000/Accepted 15 June 2001
Several characteristics of Mycobacterium tuberculosis (e.g., conserved genome and low growth rate) have severely restricted the study of the microorganism. The discovery of IS6110 raised hopes of overcoming these obstacles. However, our knowledge of this IS element is relatively limited; even its two basic characteristics (transposition mechanism and target site selection) are far from well understood. In this study, IS6110 insertions in ipl loci (iplA and iplB) in two collections of clinical isolates of M. tuberculosis from different geographic locations, one from Scotland and the other from Thailand, were investigated. Five different IS6110 insertions in the loci were identified: ipl-4::IS6110, ipl-5::IS6110, ipl-11::IS6110, ipl-12::IS6110, and ipl-13::IS6110. An attempt to establish the phylogenetic relationship of the isolates containing these insertions was unsuccessful, suggesting that some of these insertions may have arisen from more than one event. This possibility is further supported by the observation that IS6110 copies existed in the same site but with different orientations in different isolates, and the insertion site of ipl-1::IS6110 harbored IS6110 copies in both iplA and iplB in different strains. All these suggest the independent occurrence of IS6110 insertions at the same sites of the genome of M. tuberculosis in different clinical isolates. The implications of this finding are discussed.
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