Bakuchiol perturbs purine metabolism and ABC transporter pathways in Streptococcus agalactiae, possibly affecting S. agalactiae-induced mastitis

Objective To evaluate the bacteriostatic effect of Bakuchiol (Bak) against Streptococcus agalactiae , explored its antibacterial mechanism in vitro , and investigated its in-vivo therapeutic activity in a mouse mastitis model. Methods The Oxford cup assay was performed to test its inhibitory activity on S. agalactiae . Scanning electron microscopy and qPCR were employed to unravel the in-vitro molecular mechanism of Bak. Metabolomics was conducted to assess the impact of Bak on bacterial metabolites. A S. agalactiae -induced mouse mastitis model was constructed, and its therapeutic efficacy in mice was evaluated via histopathological sections and detection of inflammatory cytokine (IL-6, IL-8, IL-1β and TNF-α) expression. Results Among 24 natural small-molecule phenolic compounds, Bak exhibited favorable antibacterial activity against Streptococcus agalactiae . Mechanistic studies revealed that Bak significantly inhibited the production of virulence factors and the expression of virulence genes. Notably, it suppressed biofilm formation by disrupting initial adhesion, eliminating mature biofilms, and reducing biofilm metabolism and extracellular polymer production. Untargeted metabolomics analysis revealed that Bak might produce antibacterial activity through significant disruption of purine metabolism and ABC transport-associated metabolic pathways in S. agalactiae . Acute toxicity studies indicated that Bak exhibited low toxicity. In a mouse mastitis model, Bak significantly improved mastitis by mitigating tissue damage, and downregulating pro-inflammatory cytokine levels. Conclusion Bak attenuated S. agalactiae pathogenicity through a multi-target mechanism, positioning it as a potential therapeutic candidate for bacterial mastitis.