ICE SXT vs. ICESh95: Co-existence of Integrative and Conjugative Elements and Competition for a New Host.

Integrative and conjugative elements (ICEs) are mobile genetic elements that contribute to horizontal gene transfer. The aim of this work was to study different types of ICEs in clinical isolates of the emergent pathogen Shewanella spp., to compare their transfer efficiency and their ability to integrate a new host. Here we show that 3 out of 10 clinical isolates contained an ICE. Two of these elements were similar to ICEs from the SXT/R391 family and the other one was similar to ICESh95, a hybrid platform. Mating assays showed that these elements co-exist for several generations in the same host. Furthermore, transfer rates and competition assays between ICESh95 and ICESh392, an SXT-like element, suggest that the latter has evolved into a well-oiled machine that efficiently spread to different bacteria. Our results provide strong evidence of the role that ICEs play in the dissemination of genetic traits in nature and the implications that they have in the global threat of antimicrobial resistance.