Antibiofilm and antibacterial activities of lupinifolin in combination with protein synthesis inhibitors against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA)-derived biofilm formation is a crucial virulence factor, which essentially contributes to therapeutic challenges. This study aims to evaluate the antibiofilm and antibacterial formation activities of lupinifolin, a prenylated flavanone derived from Derris reticulata Craib. stem, in combination with protein synthesis inhibitors.

The crystal violet biofilm formation assay was performed to determine the biofilm formation activity. The synergistic antibacterial activities were evaluated using the checkerboard and time-kill assays.

Lupinifolin and tetracycline significantly reduced MRSA biofilm formation with IC50 values of 15.32 ± 5.98 and 13.42 ± 5.90 µg/mL, respectively. On the contrary, the individual treatment of streptomycin and clindamycin tended to enhance biofilm formation. Lupinifolin at the sub-MIC of 8 µg/mL in combination with certain sub-MICs of tetracycline (8 and 16 µg/mL), streptomycin (16, 32, and 64 µg/mL), or clindamycin (4, 8, and 16 µg/mL) caused significant inhibitions against MRSA biofilm formation (P<0.05). The combination of lupinifolin and streptomycin exhibited a synergy (FIC index <0.625), confirmed in the time-kill assay. Conversely, the combination of lupinifolin and tetracycline or clindamycin resulted in no interaction (FIC indices of 1.0078 and <1.0156, respectively).

The antibacterial synergy of lupinifolin and streptomycin possibly contributed to their antibiofilm-forming activity. However, the combinations of lupinifolin and tetracycline or clindamycin conceivably executed their antibiofilm activity directly against the MRSA biofilm formation process. These findings indicate a potential role for lupinifolin as an antibiofilm enhancer to diminish MRSA biofilm formation.