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

Introduction: 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. methods: 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. results: 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). conclusion: 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.