Oxidative Stress-Mediated Antibacterial Activity of the Total Flavonoid Extracted from the Agrimonia pilosa Ledeb. in Methicillin-Resistant Staphylococcus aureus (MRSA)

(1) Background: Methicillin-resistant (MRSA) is a zoonotic pathogen that causes endocarditis, pneumonia, and skin diseases in humans and livestock. (2) Methods: The antibacterial effect of the total flavonoid against MRSA (ATCC43300) extracted from the Ledeb. ( Ledeb) was evaluated by the microdilution method. The oxidative stresses in MRSA were evaluated by the levels of intracellular hydrogen peroxide (H O ), reactive oxygen species (ROS), and oxidative stress-related genes. The DNA oxidative damage was tested by the 8-hydroxy-2'-deoxyguanosine (8-OHdG) and DNA gel electrophoresis. The differentially expressed proteins were determined by the method of SDS-PAGE and NanoLC-ESI-MS/MS, while the mRNAs of differential proteins were determined by Real-Time PCR. The changes of ultra-structures in MRSA were observed by Transmission Electron Microscope (TEM). (3) Results: The minimum inhibitory concentration (MIC) of the total flavonoid against MRSA was recorded as 62.5 μg/mL. After treatment with the total flavonoid, the levels of intracellular H O and ROS were increased and the gene expressions against oxidative stress ( , , ) were decreased ( < 0.01), while the gene expression for oxidative stress ( ) was increased ( < 0.01). The level of intracellular 8-OHdG in MRSA was increased ( < 0.01) and the DNA was damaged. The results of TEM also showed that the total flavonoid could destroy the ultra-structures in the bacteria. (4) Conclusions: The total flavonoid extracted from the Ledeb can induce the oxidative stress that disturbed the energy metabolism and protein synthesis in MRSA.