Inhibitory effects of extracts from Prunella vulgaris on biofilm formation of Staphylococcus aureus.

Staphylococcus aureus (S. aureus) is a highly prevalent pathogen capable of strongly adhering to food processing equipment and the contact surfaces, where it forms resilient biofilms that are difficult to eliminate. Prunella vulgaris (P. vulgaris), a traditional Chinese herbal medicine, has demonstrated strong potential in inhibiting S. aureus biofilm formation. This study investigated the inhibitory mechanisms of P. vulgaris extracts against S. aureus growth and biofilm formation, evaluating the biofilm inhibitory concentration, bactericidal concentration and their effects on ica operon gene expression. The P. vulgaris extracts exhibited a minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 1.25 mg/mL. At the MIC level, the extracts not only suppressed S. aureus growth and metabolic viability but also inhibited polysaccharide intercellular adhesion (PIA), prevented biofilm formation and disrupted mature biofilms. Furthermore, P. vulgaris extracts demonstrated concentration-dependent effects on extracellular polymeric substances (EPS) production: while 1/2 MIC concentrations stimulated EPS synthesis, double-MIC concentrations markedly suppressed it. Notably, the extracts consistently downregulated icaA and icaD expression at both MIC and 2 × MIC concentrations. Therefore, P. vulgaris exhibits significant potential against S. aureus-induced foodborne diseases, demonstrating promise as a novel antibacterial agent for future applications in both pharmaceutical development and food safety enhancement.