The aim of our works was to explore mobile genetic elements (MGE), involved in antibiotic resistance. Indeed, resistance determinants arise either from chromosomal mutations or from gene acquisition. Most acquired resistance genes are thought to have been transferred by integrase or transposase from the chromosome of environmental microorganisms to MGE [plasmids, transposons, insertion sequences (IS), integrons] which subsequently spread through human and/or animal pathogenic bacteria. DNA mobilization of these MGE involved bacterial enzymes that could share gene transfer mechanisms with viral or eukaryotic enzymes.
We first focused on the bacterial integrase (IntI1) encoded by a class 1 integron, characterized in a clinical strain of Pseudomonas aeruginosa. IntI1 was expressed, purified and used in the first biochemical test mimicking the in vitro recombination activity catalyzed by the enzyme (Dubois et al, 2007a). This biochemical assay allowed us to determine the recombination mechanism catalyzed by IntI1 and identify the active oligomeric complexes involved on the different recombination sites (Dubois et al, 2009). Some observations showed that Int1 in particular context seems to be inactive (Dubois et al, 2007b), and led us to explore the regulation of IntI1 expression by analysis the role of some chaperon proteins in the recombination catalyzed by IntI1. Cellular control of this activity by DNA maintenance bacterial proteins was also further determined (Loot et al., 2013).
The analysis of additional types of gene transfer will provide a broader view on the genome mobility processes. In this context, we have also initiated the study of the transposition mediated by the transposase belonging to the IS91 family. By sequence homologies, it seems related to members of the REP family of replication proteins using the rolling-circle replication. An in vivo transposition test with IS1294, a representative of the IS91 family, has been developed and pointed the importance of ends of IS1294 in transposition mechanism. By a one-end transposition, we showed that the IS1294 was responsible for resistance genes mobilization between conjugative plasmids belonging to different incompatibility groups (Yassine et al, en preparation).
Surveillance of antibiotic resistance evolution is critical for delineating first-line prescription, and monitoring multi-drug resistant bacteria dissemination. We conducted epidemiological studies in health care centers and community setting (Ben-Ami et al, 2009, Arpin et al, 2009), that supported the view of the resistance spread from environmental microorganisms by demonstrating the existence of extra-hospital reservoirs (environment, animal, community) of the resistance genes. Moreover, the characterization of several mechanisms of resistance (Arpin et al, 2012a) and the description of their location within MGE (Dubois et al, 2010) allowed us to underline the strong potential of MGE in diffusion of resistance genes and the broad distribution of these MGE among resistant strains. We also described the organization or the evolution of some MGE, as bacterial integrons (Dubois et al, 2007b) and plasmids responsible for the emergence of new resistance mechanisms in clinical strains (Arpin et al, 2012a, 2012b). These descriptions highlighted the strong MGE adaptability leading to multidrug resistant strains that cause serious therapeutic problems.