Brazilin reduces methicillin-resistant Staphylococcus aureus virulence and pathogenicity by decreasing the secretion...

Methicillin-resistant Staphylococcus aureus (MRSA) is a super-resistant bacterium with strong pathogenicity, causing broad range of infections in various tissues. α-Hemolysin (Hla) is the main virulence factor of S. aureus. Brazilin (BN), is a homoisoflavonoid derivative, obtained from the wood of Caesalpinia echinata Lam (Brazil-wood), Caesalpinia sappan L (Leguminosae), and Caesalpinia violacea Standl, has been proven to exert excellent antibacterial and anti-virulence effects against S. aureus. However, the underlying mechanisms remain still unclear.

This study aims to evaluate the inhibitory effect of BN on MRSA virulence and pathogenicity and elucidate its underlying mechanisms.

Rabbit erythrocytes were used to evaluate the effect of BN on hemocytolysis. The potential target of BN was screened by transcriptomic sequencing and verified by qRT-PCR, western blot (WB), and molecular interaction experiments. The effects of BN on MRSA toxicity and pathogenicity were both validated using A549 cell and mouse skin abscess model caused by MRSA.

BN attenuated the hemolytic activity of MRSA by inhibiting Hla secretion. It was also found that BN blocks its binding to the P1 promoter of the sae operon, and then reduced its transcript level. Remarkably, ΔsaeR strain exhibits significantly reduced hemolytic activity due to impaired regulation of Hla and no extra inhibitory effect was observed in the samples treated with BN. Moreover, BN relieved A549 cell damage and mouse skin abscess induced by MRSA by inhibiting SaeR.

These findings reveal, for the first time, BN can alleviate MRSA virulence and pathogenicity by decreasing the secretion of the Hla via inhibiting SaeR. Overall, this study suggests that BN could be a candidate for being submitted to further studies with the aim of its development as a new antibiotic against MRSA.