In vitro activities of isobavachalcone against planktonic and persister cells and biofilm of Enterococcus faecalis

Abstract

Background Mounting evidences have demonstrated the extensive pharmacological activities of the natural product isobavachalcone, including antimicrobial activity, inhibition of reverse transcriptase, antitubercular and antioxidant ability et al. However, the antibacterial and antibiofilm activity and its action mode of isobavachalcone against clinical E. faecalis isolates remain elusive. This study aims to evaluate the in vitro antibacterial and anti-biofilm activities of isobavachalcone on clinical E. faecalis isolates from China and further investigate the possible target site of isobavachalcone in E. faecalis. Results Our data suggested the MICs of isobavachalcone ranging from 6.25 to 12.5 µM against 220 E. faecalis strains. The robust inhibitory effect of isobavachalcone with sub-MIC concentration ( 1/2xMIC ) against the biofilm formation of E. faecalis was found. The rapid bactericidal effect of isobavachalcone against E. faecalis was demonstrated and more planktonic cells could be killed by isobavachalcone compared with vancomycin, linezolid, or ampicillin at 2, 4, 6, and 12h. No synergetic bactericidal activity of isobavachalcone combined with vancomycin, linezolid, or ampicillin was found. Furthermore, genetic mutation of isobavachalcone-resistant E. faecalis was compared with the parental strain by whole genome sequencing, showing that the functions of the mutated proteins were associated with the PurH and FlgJ proteins and other eight proteins involved in the cell wall or cell membrane biogenesis, DNA synthesis, and energy metabolism. Molecular docking analysis showed that FlgJ protein might serve as the potential target of isobavachalcone in E. faecalis. Other mutations are involved in the cell wall or cell membrane biogenesis, DNA synthesis, and energy metabolism. Conclusion This study discovered that isobavachalcone had an antibacterial effect on E. faecalis, and significantly inhibited the biofilm formation of E. faecalis at subinhibitory concentrations. In addition, antibacterial and antibiofilm activity against clinical E. faecalis isolates from China by targeting FlgJ protein.