Phytotherapeutic potential against MRSA: mechanisms, synergy, and therapeutic prospects.

Background: Rising resistance to antimicrobials, particularly in the case of methicillin-resistant Staphylococcus aureus (MRSA), represents a formidable global health challenge. Consequently, it is imperative to develop new antimicrobial solutions. This study evaluated 68 Chinese medicinal plants renowned for their historical applications in treating infectious diseases.

Methods: The antimicrobial efficacy of medicinal plants were evaluated by determining their minimum inhibitory concentration (MIC) against MRSA. Safety profiles were assessed on human colorectal adenocarcinoma (Caco-2) and hepatocellular carcinoma (HepG2) cells. Mechanistic insights were obtained through fluorescence and transmission electron microscopy (FM and TEM). Synergistic effects with vancomycin were investigated using the Fractional Inhibitory Concentration Index (FICI).

Results: Rheum palmatum L., Arctium lappa L. and Paeonia suffructicosaas Andr. have emerged as potential candidates with potent anti-MRSA properties, with an impressive low MIC of 7.8 µg/mL, comparable to the 2 µg/mL MIC of vancomycin served as the antibiotic control. Crucially, these candidates demonstrated significant safety profiles when evaluated on Caco-2 and HepG2 cells. Even at 16 times the MIC, the cell viability ranged from 83.3% to 95.7%, highlighting their potential safety. FM and TEM revealed a diverse array of actions against MRSA, such as disrupting the cell wall and membrane, interference with nucleoids, and inducing morphological alterations resembling pseudo-multicellular structures in MRSA. Additionally, the synergy between vancomycin and these three plant extracts was evident against MRSA (FICI < 0.5). Notably, aqueous extract of R. palmatum at 1/4 MIC significantly reduced the vancomycin MIC from 2 µg/mL to 0.03 µg/mL, making a remarkable 67-fold decrease.

Conclusions: This study unveil new insights into the mechanistic actions and pleiotropic antibacterial effectiveness of these medicinal plants against resistant bacteria, providing robust evidence for their potential use as standalone or in conjunction with antibiotics, to effectively combat antimicrobial resistance, particularly against MRSA.