Importance of integrons in the diffusion of resistance

Horizontal transfer of resistance genes is a successful mechanism for the t ransmission and dissemination of multiple drug resistance among bacterial p athogens. The impact of horizontally transmitted genetic determinants in th e evolution of resistance is particularly evident when resistance genes are physically associated in clusters and transferred en bloc to the recipient cell. Recent advances in the molecular characterisation of antibiotic resi stance mechanisms have highlighted the existence of genetic structures, cal led integrons, involved in the acquisition of resistance genes. These DNA e lements have frequently been reported in multi-drug resistant strains isola ted from animals and humans, and are located either on the bacterial chromo some or on broad-host-range plasmids. The role of integrons in the developm ent of multiple resistance relies on their unique capacity to cluster and e xpress drug resistance genes. Moreover, the spread of resistance genes amon g different replicons and their exchange between plasmid and bacterial chro mosome are facilitated by the integration of integrons into transposable el ements. The association of a highly efficient gene capture and expression s ystem, together with the capacity for vertical and horizontal transmission of resistance genes represents a powerful weapon used by bacteria to combat the assault of antibiotics.