Screening of Antimicrobial Ingredients in Forsythia Leaves Using Target Constituent Knock-out/Knock-in Strategy and Evaluation of the Combination Effects with Antibiotics

To screen and identify the antimicrobial ingredients of Forsythia suspensa leaves (FL). A screening method based on a constituent knock-out/knock-in strategy was conducted. The antimicrobial activities of FL components against seven commonly infective strains were determined using the Oxford cup method. Their antimicrobial effects when used in combination with common antibiotics were investigated by a checkerboard titration method. Two of the seven strains, Staphylococcus aureus and methicillin-resistant S. aureus (MRSA), were considered to be the most sensitive to the inhibitory effect of FL. The main antimicrobial components in FL were forsythoside I and forsythoside A. The co-administration of vancomycin with forsythoside A was found to have a significant synergistic inhibiting effect on MRSA. Some phenylethanol glycoside components play a major contribution to the antimicrobial effect of FL. This provides a reference for the research and development of FL for both medicinal and food purposes.