Integrative Conjugative Elements (ICEs) of the SXT/R391 group as vehicles for acquisition of resistance determinants, stable maintenance and transfer to a wide range of enterobacterial pathogens

Integrative conjugative elements (ICEs) belonging to the SXT/R391 group of mobile drug resistance elements are predominantly found in enterobacterial pathogens of human and waterborne origin. A key feature of such elements is their ability to stably integrate into their host prfC gene, initially truncating the gene but restoring prfC function by generating a novel hybrid prfC gene upon integration [1, 2]. Such stable integration into the genome of host organisms has consequences for the maintenance and spread of encoded antibiotic resistance determinants. We have surveyed the nature of prfC genes containing the unique SXT/R391 group 17bp integration site and demonstrate the breadth of possible ICE hosts amongst the enterobacteria. Many ICEs encode a range of antibiotic resistance determinants which appear to become associated with particular genomes through transposition or targeted integration into specific ICE hotspots [3, 4]. We have analysed the nature of these antibiotic resistance determinants amongst sequenced ICEs and have observed specific patterns of resistance and resistance determinant location. Interestingly, many ICE elements encode rumAB genes, which encode a mutagenic polymerase, polV that appears to be a targeted hotspot for insertion of many resistance determinants [5, 6]. A rational for insertion into such hotspots is discussed.