DNA insertion sequences and the molecular epidemiology of Salmonella and Mycobacterium

The general characteristics and genetics of insertion sequence (IS) elements are well-established. For Escherichia coli IS elements, mechanisms of transposition and mutation are known and their recombinogenic role in the bacterial genome has been investigated. Population models relate the distribution of these IS elements to autoregulation of their transposition. IS200, the smallest known element, is confined to the salmonellae and several lineages of E. coli. It exhibits atypical molecular features. The population dynamics of IS200 make it a particularly effective marker of chromosomal genotype in many Salmonella serovars. Molecular epidemiological typing with IS200 has been developed for important serovars in groups D1, C1, C2 and B. Findings for S. Enteritidis, S. Panama, S. Infantis, S. Typhimurium, S. Heidelberg, S. Paratyphi B and S. Java are reviewed. Of the 12 IS elements found in mycobacteria, IS6110, found in Mycobacterium tuberculosis and M. bovis, exhibits the greatest potential for molecular epidemiological applications. Although M. tuberculosis is a single serogroup, and its genome is otherwise highly homogeneous, strains are highly polymorphic with respect to copy number and location of IS6110. A standard IS6110 typing method has been established, together with novel PCR-based approaches to IS6110 fingerprinting.