Synergistic effect on anti-methicillin-resistant Staphylococcus aureus among combinations of α-mangostin-rich extract, lawsone methyl ether and ampicillin.

α-Mangostin rich extract (AME) exhibited satisfactory inhibitory activities against all tested MRSA strains, with minimum inhibitory concentrations (MICs) of 7.8-31.25 µg/mL, while lawsone methyl ether (LME) and ampicillin revealed weak antibacterial activity with MICs of 62.5-125 µg/mL. However, the combination of AME and LME showed synergistic effects against all tested MRSA strains with fractional inhibitory concentration index (FICI) values of 0.008-0.009, while the combination of AME and ampicillin, as well as LME and ampicillin produced synergistic effects with FICIs of 0.016-0.257. A time-kill assay against MRSA (DMST 20654 strain) revealed a 6-log reduction in CFU/mL, which completely inhibited bacterial growth for the combinations of AME and LME, AME and ampicillin, and LME and ampicillin at a 8 h incubation, while those against MRSA (2468 strain) were at 10 h incubation. The combination of α-mangostin and LME as well as the combinations of each compound with ampicillin synergized the alteration of membrane permeability. In addition, α-mangostin, LME and ampicillin inhibited the biofilm formation of MRSA. These findings indicated that the combinations AME and LME or each of them in combination with ampicillin had enhanced antibacterial activity against MRSA. Therefore, these compounds might be used as the antibacterial cocktails for treatment of MRSA.