C. jejuni exhibits outstanding genetic diversity primarily due to frequent natural transformation. Routine monitoring of antibiotic resistance in Campylobacter performed in the National Reference Laboratory for Campylobacter revealed that a high percentage of isolates from food are resistant against multiple antimicrobials. Extracellular DNA can serve as nutrient source, matrix for biofilm formation, repair of genetic damage and genome variation, leading to improved adaptation and survival of pathogens. In this sub-project, we intend to address the impact of horizontal gene transfer on genetic diversity in C. jejuni and intend to open up strategies for reduction of genetic diversity/ survival by inhibiting DNA binding and/ or uptake. This strategy might be applicable to reduce resistance spreading, biofilm formation, survival in the environment and colonisation in the host. In particular, a single cell assay will be applied for the monitoring of DNA uptake in C. jejuni, which allows for the characterisation of competence development. In addition, mutants defective in natural transformation will be tested (i) for their ability to form biofilms, (ii) for their colonisation capacity in vivo and (iii) their adaptive potential with and without selection pressure, (iv) their survival/ tenacity in the environment.