Low-concentration iron promotes Klebsiella pneumoniae biofilm formation by suppressing succinic acid

Abstract Background Klebsiella pneumoniae is widely distributed in water and plays a major role in both human and poultry infections. Many K. pneumoniae strains form biofilms on various surfaces, enhancing their pathogenicity and resistance to antibiotics. The water supply pipeline of chicken farms has become a hotbed for the growth of K pneumoniae biofilm because of its humid environment, and because the chicken drinking water pipeline is thin, it is easily blocked by the biofilm, and the diffused cells can cause repeated and persistent infections. Iron is vital to the growth of microorganisms and the formation of biofilms. Therefore, the aim of this study was to examine the effects of iron on K. pneumoniae biofilm formation and any associated metabolic changes to provide a rationale for reducing the formation of biofilms. Results Biofilm formation was enhanced to the greatest extent by the presence of 0.16 mM FeCl2, producing a denser structure under electron microscopy. The number of biofilm-forming and planktonic bacteria did not change, but protein and polysaccharide concentrations in the bacterial extracellular polymeric substances (EPS) were significantly increased by iron supplementation. To clarify this mechanism, intracellular metabolomic analysis was carried out, showing that the differential, down-regulated metabolites included succinic acid. The addition of 1.7 mM succinic acid counteracted the biofilm-forming effect of iron, with no bactericidal side effects. Conclusion This study demonstrates the importance of succinic acid and iron in K. pneumoniae biofilms, and provides insight into the formation of K. pneumoniae biofilms and direction for the development of new antibacterial agents.