['One of the most important resistance mechanisms in bacteria is the increased expression of multidrug efflux pumps. To combat efflux-related resistance, the development of new efflux pump inhibitors is essential.', 'Ten phosphorus ylides were compared based on their MDR-reverting activity in multidrug efflux pump system consisting of the subunits acridine-resistance proteins A and B (AcrA and AcrB) and the multidrug efflux pump outer membrane factor TolC (TolC) of Escherichia coli K-12 AG100 strain and its AcrAB-TolC-deleted strain. Efflux inhibition was assessed by real-time fluorimetry and the inhibition of quorum sensing (QS) was also investigated. The relative gene expression of efflux QS genes was determined by real-time reverse transcriptase quantitative polymerase chain reaction.', 'The most potent derivative was Ph'] Do fluorinated Beta-diketo Phosphorus Ylides Are Novel Efflux Pump Inhibitors in Bacteria?