In vitro antibacterial and antibiofilm activity of isolated compounds from Eriobotrya japonica leaves against Proteus mirabilis.

Loquat (Eriobotrya japonica) is a perennial tree, commonly grown as an ornamental plant and is known for its sweet edible fruits. Considering the traditional uses of medicinal plants, the aim of this study is the evaluation of the antibacterial action of isolated compounds from Eriobotrya japonica leaves. Six compounds were identified, including oleanolic acid (1), corosolic acid (2), trans-cinnamic acid (3), trans-sinapic acid (4), fisetin (5), and rutin (6). For the first time compound 5 was identified in this plant. The antibacterial effect of the two major compounds 1 and 6 was examined against Proteus mirabilis by applying the agar well diffusion method. Their minimum inhibitory concentrations (MICs) were then detected using broth microdilution assay. Rutin and oleanolic acid revealed MICs values ranging from 32 to 128 µg/mL and 512 to 2048 µg/mL, respectively. In addition, the antibiofilm action of the tested compounds was elucidated by crystal violet assay. Rutin exhibited antibiofilm activity, reducing the number of strong and moderate biofilm-forming isolates from 76.92% to 23.08%. Molecular analysis revealed that rutin downregulated mrpA, pmfA, and luxS gene expression in biofilm-forming P. mirabilis isolates. Further research is needed to explore the clinical implications of rutin.