Potentiating activity of rhein in targeting of resistance genes in methicillin-resistant Staphylococcus aureus

Objective: To investigate the synergistic effect between rhein (RHE) and oxacillin against Staphylococcus aureus (MRSA) at the gene level. Method: A minimum inhibitory concentration and checkerboard dilution test were conducted to evaluate antibacterial activity. Reverse transcriptase polymerase chain reaction was conducted to investigate the gene expressions. Results: RHE exhibited a minimum inhibitory concentration of 62.5-250.0 μg/mL against various MRSA strains and the reference strain, respectively. As revealed by the checkerboard assay, a combination of RHE and oxacillin exhibited synergistic or partially synergistic effects against MRSA strains. RHE decreased the expressions of mecA/blaZ in a dose-dependent manner. RHE also decreased the expressions of the regulator genes mecI/blaI and mecR1/blaR1. Conclusions: We suggest that RHE affects the activity of mecR1/blaR1, which is located in the cell membrane of MRSA and results in the suppression of mecA/mecI/mecR1 and blaZ/blaI/ blaR1 gene expressions.