Antibacterial activity and underlying mechanism of Meconopsis quintuplinervia Regel extract against the acne-causing bacteria Propionibacterium acnes and Staphylococcus aureus

Abstract The aim of this study was to evaluate the antibacterial activity and underlying mechanism of ethanol extracts of Meconopsis quintuplinervia Regel (EMQ) against the acne-causing bacteria Propionibacterium acnes and Staphylococcus aureus. The diameter of the inhibition zone (DIZ), minimum inhibitory concentration (MIC), and minimum bactericide concentration (MBC) were determined and growth curves were generated to assess the antibacterial activity of EMQ. The antibacterial mechanism was explored based on morphological observations, staining of the cell membrane and wall, protein analysis, and biofilm formation. The study results indicated that EMQ was an effective antibacterial agent against P. acnes and S. aureus, with a DIZ of 14.5 and 13.2 mm, MIC of 12.5 and 12.5 mg/mL, and MBC of 100 and 50 mg/mL, respectively. EMQ induced morphological changes to bacterial cells, as determined by electron microscopy. Leakage of alkaline phosphatase and nucleic acids confirmed that EMQ compromised the membrane integrity of bacterial cells. Furthermore, protein analysis revealed that EMQ hindered total protein expression and lowered adenosine triphosphatase activity, while crystal violet staining revealed suppressed biofilm production. Bacterial adhesion analysis demonstrated that EMQ lowered the adhesive capacity of bacterial cells. Collectively, these findings revealed high antibacterial activity of EMQ for treatment of acne vulgaris.