Phloretin Targets Polyphosphate Kinase 1 to Attenuate Acinetobacter baumannii Virulence and Persistence In Vitro and In Vivo

Abstract

Acinetobacter baumannii (A. baumannii) is well known for its virulence and persistence, particularly in intensive care units. Therefore, new strategies and candidates to treat A. baumannii infection are urgently needed considering the emergence of drug-resistant bacteria. Polyphosphate kinase 1 (PPK1) is required for bacterial survival as it is involved in maintaining antibiotic resistance or tolerance, pathogenesis, and adversity resistance. Multiple phenotypic assays related to virulence and persistence were performed in this study, and phloretin was shown to attenuate A. baumannii virulence and persistence by inhibiting PPK1 activity. Phloretin hampered mobility, interfered with biofilm formation and decreased resistance to ampicillin, heat, and hydrogen peroxide stress in A. baumannii. The therapeutic effect was also examined in a mouse pneumonia infection model. Molecular simulation and site-directed mutagenesis revealed that ARG-22, MET-622, ASN-57, and ARG-65 were the sites of phloretin action against PPK1. Phloretin treatment led to changes in metabolic pathways associated with A. baumannii virulence and persistence, including glycerophospholipid metabolism and fatty acid biosynthesis. Furthermore, phloretin alleviated pneumonic injury in a mouse pneumonia infection model in vivo, indicating that phloretin is a promising compound for preventing A. baumannii infection resistance by targeting PPK1.