Daphnetin as a novel polyphosphate kinase inhibitor to combat Salmonella infection

Salmonella, an important zoonotic pathogen, has attracted widespread attention due to its pathogenicity and drug resistance. The complexity of treatment options necessitates the development of new anti-infective strategies and drugs. Polyphosphate kinase (PPK), an enzyme involved in polyphosphate synthesis, plays an important role in various physiological processes. In this study, Daphnetin (DAP) was identified as a PPK inhibitor, with an IC₅₀ value of 17 μg/mL based on enzyme inhibition assays. DAP was found to inhibit bacterial motility, biofilm formation and stress resistance while also exhibiting the cellular protective effects against Salmonella infection. Molecular dynamics simulations and fluorescence quenching assays confirmed a direct interaction between DAP and PPK, specifically targeting the L590 and I41 amino acid residues, altering its conformational stability. In vivo studies using the Galleria mellonella model and a murine colitis model showed that DAP significantly improved survival rates by 60% and reduced bacterial burden in the liver, spleen and colon. Furthermore, the therapeutic effects of DAP were confirmed in a S. Pullorum infection model, further highlighting its potential as a novel therapeutic agent. Collectively, our findings suggest that targeting PPK with DAP may provide a promising strategy for treating Salmonella infections, especially in the context of increasing antibiotic resistance.