Antimicrobial activity and mechanism of tea pigments derived from the discarded tea plant branches and leaves against methicillin-resistant Staphylococcus aureus

Microbial contamination in food can cause foodborne illnesses, particularly methicillin-resistant Staphylococcus aureus (MRSA), which poses a serious threat to human health due to its ability to produce heat-resistant enterotoxins and express the broad-spectrum antibiotic resistance protein penicillin-binding protein 2a (PBP2a). In this study, tea pigments with potent anti- MRSA activity were prepared from discarded tea plant branches and leaves via in vitro enzymatic oxidation. Optimal process conditions obtained through response surface methodology (RSM) were: enzyme substrate ratio of 0.6 U/mg, reaction temperature of 43 °C, and reaction time of 22 h, yielding a production rate of 7.88%. Theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs) isolated and purified via organic solvent extraction and macroporous resin D101 exhibited similar phenolic compound spectral characteristics, with average molecular weights (Mw) of 208, 368, and 16,064 Da, respectively. The minimum inhibitory concentration (MIC) of TFs, TRs, and TBs against MRSA were 156.25, 312.5, and 1250 μg/mL, respectively, demonstrating excellent anti- MRSA activity that was significantly stronger than their inhibitory activity against Escherichia coli . Furthermore, tea pigments exert antibacterial effects through mechanisms including cell wall disruption, alteration of cell membrane permeability, inhibition of biofilm formation, reduction of respiratory chain dehydrogenase activity, and increased levels of intracellular reactive oxygen species in bacteria. Additionally, molecular docking indicates that theaflavins effectively binds to PBP2a, thereby interfering with MRSA growth. Tea pigments as anti- MRSA natural products have great prospects in food industry.