Synergistic antibacterial effects of Buddleja albiflora metabolites with antibiotics against Listeria monocytogenes.

Some plants of Buddleja genus possessed antimicrobial activity. In this study, the antibacterial activities of nine compounds from Buddleja albiflora were evaluated against Listeria monocytogenes, Staphyloccocus aureus, Escherichia coli and Pseudomonas aeruginosa, either alone or in combination with Erythromycin (Ery), Gentamicin (Gen) and Ampicillin (Amp). Checkerboard assay demonstrated that Kumatakenin elicited synergistic effects with all three antibiotics, and chrysin displayed synergistic effect with Ery against L. monocytogenes. Further experiments showed that the synergy effect was sufficient to eradicate biofilms formed by L. monocytogenes. Thus, our data highlighted that the combinations of secondary metabolites from B. albiflora and specific antibiotics were useful for the treatment of pathogens, which might help prevent the spread of antibiotic resistance through improving antibiotic effectiveness. SIGNIFICANCE AND IMPACT OF THE STUDY: This study measured the antibacterial activity of the metabolites from Buddleja albiflora and the synergistic interactions with antibiotics against Listeria monocytogenes on planktonic cells as well as on biofilms. The results of this study provide valuable evidence that Kumatakenin/antibiotic combination can be considered as a promising antimicrobial agent for the treatment of pathogens, which subsequently help prevent the spread of antibiotic resistance through improving antibiotic effectiveness.