Enterobacteriaceae producing ESBL (ESBL-E) are a major public health problem leading to an increase of morbi-mortality. Enterobacteriaceae can adapt to their hosts and/or hospital environment through diverse mechanisms, in particular modification of efflux systems expression conferring resistance to a large panel of biocides. AcrAB-TolC is a resistance-nodulation-division (RND) pump, which is in part regulated by a two-component system: RamAR operon. Mutations in this operon drive to a pump over-expression leading to a cross-resistance (CR) phenotype regarding quinolones, tigecycline, chloramphenicol, temocillin as well as a higher tolerance to biliary salts and resistance to phagocytosis. The aim of the study was to determine the prevalence of the mutations inside the RamAR operon leading to a CR phenotype among ESBL-E isolated and sequenced in a French Teaching hospital.