Dissemination and Evolution of resistance integrons: impact of bacterial lifestyle and antibiotic stress – DIVIN

The World Health Organization has declared antimicrobial resistance one of the biggest threats to modern health. Resistance integrons are genetic platforms allowing bacteria to adapt rapidly to antibiotic pressure through acquisition, stockpiling and expression of antibiotic resistance gene cassettes. Mainly located on mobile genetic elements, resistance integrons are low-cost structures that greatly participate to the dissemination of multidrug resistance among clinically relevant Gram-negative pathogen bacteria. Most bacterial infections are caused by pathogen living in biofilms, the natural bacterial lifestyle in most ecosystems. As compared to planktonic conditions, biofilm is known favor horizontal transfers of mobile genetic elements as well as bacteria survival in the presence of antibiotics. Accordingly, the biofilm lifestyle may favor evolutionary trajectories towards antibiotic resistance that differ from those generally described in planktonic cultures. Also, in nature, bacteria are frequently exposed to sub-inhibitory antibiotic concentrations owing to antibiotic treatment remnants or environmental pollution. The main objective of the DIVIN project is to investigate the impact of biofilms and sub-inhibitory concentrations of antibiotics on the evolution of resistance integrons in terms of expression level of resistance as well as antibioresistance dissemination, with a focus on class 1 resistance integrons that are highly associated with multidrug resistance in clinical settings. To do so, we will construct Escherichia coli strains carrying various class 1 integron with at least one gene cassette coding for tobramycin resistance. These bacteria will then be propagated both in planktonic and biofilm conditions in the presence or absence of sub-inhibitory concentrations of antibiotics. Bacterial evolution towards increase antibiotic resistance will be assessed using flow-cytometry and next generation sequencing approaches. We will also attempt to visualize the exchange of gene cassettes between bacteria in the biofilm using a microfluidic set-up associated to confocal microscopy. The results of the DIVIN project should allow us to evaluate whether the biofilm lifestyle associated to sub-inhibitory concentrations of antibiotic favor i) the evolution of bacteria carrying resistance integron toward phenotypes of higher resistance and ii) horizontal gene transfer of genetic determinants of resistance. A better understanding of the adaptive potential of integron-positive bacteria should help identifying new ways to prevent antibiotic resistance acquisition/spread in biofilms which are a real burden in clinical settings.