Antibacterial activity of Chinese propolis and its synergy with β-lactams against methicillin-resistant Staphylococcus aureus.

Propolis has exhibited effective antibacterial activities in preventing the growth of multiple pathogenic bacteria. However, the antibacterial activity of Chinese propolis against methicillin-resistant Staphylococcus aureus (MRSA) is almost unknown. The present study aimed to explore the antibacterial activity and action mechanism of Chinese propolis ethanol extract (CPEE) against MRSA. Thirteen compounds of CPEE were identified using HPLC-DAD/Q-TOF-MS, and none of them showed better anti-MRSA activity than CPEE. The diameter of inhibition zone (DIZ) of CPEE was 20.1 mm. The minimal inhibitory concentration (MIC) of CPEE was 32 mg/L, while the minimal bactericidal concentration (MBC) against MRSA was 64 mg/L. Moreover, CPEE showed significant synergistic effects with β-lactam antibiotics (ampicillin and oxacillin). Nucleic acid and protein leakage assays showed that CPEE can stimulate the release of intracellular macromolecules by damaging the cell membrane integrity of MRSA. Live/dead-staining and SDS-PAGE assays further confirmed that CPEE could inhibit bacterial activities by disrupting the membrane. The reduction in PBP2a expression and β-lactamase activity, as shown by western blot and β-lactamase detection assays, suggested that CPEE was able to reverse the drug resistance of MRSA. These results demonstrated the anti-MRSA activity of CPEE was mainly due to changing the cell membrane and reversing resistance, which indicates that CPEE could be an attractive candidate for use in future food and medical applications.