Penfluridol synergizes with colistin to reverse colistin resistance in Gram-negative bacilli

The growing prevalence of antibiotic resistance in multidrug-resistant Gram-negative bacteria (MDR-GNB), exacerbated by the misuse of antibiotics, presents a critical global health challenge. Colistin, a last-resort antibiotic for severe MDR-GNB infections, has faced diminishing efficacy due to the emergence of colistin-resistant (COL-R) strains. This study evaluates the potential of penfluridol (PF), an antipsychotic drug with notable antibacterial and antibiofilm properties, to restore colistin activity against COL-R GNB in vitro. PF alone exhibited limited antibacterial activity against COL-R GNB; however, its combination with colistin demonstrated strong synergistic effects, significantly reducing colistin's minimum inhibitory concentrations (MICs) by 4-128 times. Time-kill assays confirmed the combination's superior bactericidal activity compared to either agent alone. Membrane permeability assays revealed that PF enhanced colistin's ability to disrupt bacterial membranes, likely by facilitating colistin binding to lipopolysaccharide. Furthermore, PF significantly inhibited the development of colistin resistance over a 30-day resistance development assay. In addition to its antibacterial effects, PF exhibited notable antibiofilm activity. The combination of PF and colistin effectively inhibited biofilm formation and eradicated mature biofilms in most of the tested COL-R GNB strains. These findings mark the first report of PF's synergistic interaction with colistin against GNB biofilms, offering a promising strategy to combat biofilm-associated infections. Overall, the colistin/PF combination holds potential as an effective therapeutic strategy to enhance colistin efficacy, delay resistance development, and manage biofilm-associated infections in MDR-GNB.