Formononetin disrupts MRSA biofilm via potential SarA-associated regulatory modulation

Biofilm formation is a crucial aspect of Methicillin-resistant Staphylococcus aureus (MRSA) pathogenesis and contributes to its resistance against conventional antibiotics. This study reports the identification of a bioactive molecule, formononetin, from Glycyrrhiza glabra L., that is effective against MRSA. Formononetin significantly inhibited biofilm formation, disrupted sessile biofilm, and reduced the hemolytic activity of MRSA in a dose-dependent manner. Formononetin also increased the survival rate of MRSA-infected G. mellonella larvae by decreasing the bacterial load and increasing melanization. The combination of formononetin with antibiotics, like oxacillin, ampicillin, and streptomycin, showed a fractional inhibitory concentration index (FICI) ≤ 0.5, which indicates a synergistic effect. Molecular docking studies showed formononetin can bind to the global regulator, SarA, with an estimated binding score of −6.176 kcal/mol. Further, the aspartate residue (D20) in SarA was identified as a binding site for formononetin. Microscale thermophoresis and electrophoretic mobility shift assay of the SarAD20A mutant showed reduced affinity towards formononetin without affecting its DNA-binding activity compared to its wild-type counterpart. Further, proteomic profiling of MRSA upon treatment with formononetin showed significant modulation of SarA and SarA-related pathways, such as scdA and agrC. Our findings suggest that formononetin holds promise as a natural agent for combating MRSA biofilm.