Neobavaisoflavone Inhibits Biofilm Formation and α-Toxin Activity of Staphylococcus aureus

Neobavaisoflavone had antimicrobial activities against Gram-positive multidrug-resistant (MDR) bacteria, but the effect of neobavaisoflavone on the virulence and biofilm formation of S. aureus has not been explored. The present study aimed to investigate the possible inhibitory effect of neobavaisoflavone on the biofilm formation and α-toxin activity of S. aureus. Neobavaisoflavone presented strong inhibitory effect on the biofilm formation and α-toxin activity of both methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains at 25 µM, but did not affect the growth of S. aureus planktonic cells. Genetic mutations were identified in four coding genes, including cell wall metabolism sensor histidine kinase walK, RNA polymerase sigma factor rpoD, tetR family transcriptional regulator, and a hypothetical protein. The mutation of WalK (K570E) protein was identified and verified in all the neobavaisoflavone-induced mutant S. aureus isolates. The ASN501, LYS504, ILE544 and GLY565 of WalK protein act as hydrogen acceptors to form four hydrogen bonds with neobavaisoflavone by molecular docking analysis, and TRY505 of WalK protein contact with neobavaisoflavone to form a pi-H bond. In conclusion, neobavaisoflavone had excellent inhibitory effect on the biofilm formation and α-toxin activity of S. aureus. The WalK protein might be a potential target of neobavaisoflavone against S. aureus.