Quercetin targets SarA of methicillin-resistant Staphylococcus aureus to mitigate biofilm formation

ABSTRACT The emergence of methicillin-resistant Staphylococcus aureus (MRSA) led to the failure of conventional antibiotic treatment, resulting in serious morbidity and mortality. The biofilm formation of S. aureus is a potential mechanism for drug resistance. SarA is an important regulatory protein for the formation of S. aureus biofilm. In this study, the global regulator SarA was used as a target to virtually screen natural active monomers. SarA inhibitor quercetin (QEN) was assessed. Molecular docking and kinetic simulation showed that QEN was stably bound to the formation site of SarA dimer. Spectral analysis verified that QEN was bound to SarA and changed its conformation. In vitro biofilm, the culture showed that 4 µg/mL QEN significantly inhibited biofilm formation, and the production of extracellular polymers and eDNA concentration significantly reduced. Scanning electron microscopy and laser confocal microscopy further confirmed the inhibitory effect of QEN on biofilm formation. At the same time, a decrease in the transcription level of sarA and its downstream genes related to biofilm regulation and a decrease in the expression level of SarA were also observed, confirming the QEN-induced inhibition of sarA. In conclusion, the results of this study revealed SarA-mediated anti-biofilm effect of QEN on MRSA. IMPORTANCE Anti-biofilm is an important strategy against Staphylococcus aureus chronic infection. SarA is a positive regulator of biofilm formation in S. aureus. In this study, we identified the SarA inhibitor quercetin using computer simulation screening. Previous studies have shown that quercetin inhibits biofilm; however, the underlying mechanism remains unknown. This study revealed the inhibitory effect of quercetin on the SarA protein. We also isolated the SarA protein and confirmed its interaction with quercetin in vitro. Besides, the inhibitory effect of quercetin on the transcription and translation levels of the SarA protein was also determined. The effects of quercetin on S. aureus biofilm inhibition and biofilm components were consistent with the changes in the transcription level of biofilm-related genes regulated by SarA. In summary, our study revealed the mechanism by which quercetin affects biofilm formation by inhibiting the transcriptional regulator SarA of S. aureus. Anti-biofilm is an important strategy against Staphylococcus aureus chronic infection. SarA is a positive regulator of biofilm formation in S. aureus. In this study, we identified the SarA inhibitor quercetin using computer simulation screening. Previous studies have shown that quercetin inhibits biofilm; however, the underlying mechanism remains unknown. This study revealed the inhibitory effect of quercetin on the SarA protein. We also isolated the SarA protein and confirmed its interaction with quercetin in vitro. Besides, the inhibitory effect of quercetin on the transcription and translation levels of the SarA protein was also determined. The effects of quercetin on S. aureus biofilm inhibition and biofilm components were consistent with the changes in the transcription level of biofilm-related genes regulated by SarA. In summary, our study revealed the mechanism by which quercetin affects biofilm formation by inhibiting the transcriptional regulator SarA of S. aureus.