Polyphenol Analysis and Antibacterial Potentials of Twig Extracts of Salix aurita, S. pyrolifolia, and S. caprea Growing Naturally in Finland

Abstract

Salix species have been used in traditional medicine to treat fever and inflammation. However, there is no reported information on the antibacterial activities of S. aurita and S. pyrolifolia, and little is known about the phytochemistry of S. aurita. In this study, winter-dormant twig extracts of S. aurita, S. caprea, and S. pyrolifolia were screened for their antibacterial activities against Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus cereus, and Escherichia coli. The antibacterial effects were evaluated using agar diffusion and turbidimetric microplate methods. Time-kill effects were measured using the microplate optical density (OD620) method. UPLC-PDA-QTOF/MS analysis was conducted to identify the polyphenols present in a methanol extract of S. aurita. The antibacterial results show that methanol and hot and cold water twig extracts of S. aurita, S. caprea, and S. pyrolifolia have significant antibacterial effects against P. aeruginosa, S. aureus, and B. cereus with the diameters of the inhibition zones (IZDs) ranging from 16.17 to 30.0 mm and the MICs between 1250 and 2500 µg/mL. Only the cold water extract of S. caprea was moderately active against E. coli. Proanthocyanidins, procyanidin B1 (m/z 577), and procyanidin C1 (m/z 865) were identified as the major polyphenols present in the methanol extract of S. aurita twigs for the first time. Additionally, salicin-7-sulfate was present in S. aurita twigs. Procyanidin B-1, taxifolin, trans-p-hydroxycinnamic acid, and catechin showed growth inhibitory activity against B. cereus with a MIC value of 250 µg/mL.