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

<i>Salix</i> species have been used in traditional medicine to treat fever and inflammation. However, there is no reported information on the antibacterial activities of <i>S. aurita</i> and <i>S. pyrolifolia</i>, and little is known about the phytochemistry of <i>S. aurita</i>. In this study, winter-dormant twig extracts of <i>S. aurita</i>, <i>S. caprea</i>, and <i>S. pyrolifolia</i> were screened for their antibacterial activities against <i>Pseudomonas aeruginosa</i>, <i>Staphylococcus aureus</i>, <i>Bacillus cereus</i>, and <i>Escherichia coli</i>. 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 <i>S. aurita</i>. The antibacterial results show that methanol and hot and cold water twig extracts of <i>S. aurita</i>, <i>S. caprea</i>, and <i>S. pyrolifolia</i> have significant antibacterial effects against <i>P. aeruginosa</i>, <i>S. aureus</i>, and <i>B. cereus</i> 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 <i>S. caprea</i> was moderately active against <i>E. coli</i>. Proanthocyanidins, procyanidin B1 (<i>m</i>/<i>z</i> 577), and procyanidin C1 (<i>m</i>/<i>z</i> 865) were identified as the major polyphenols present in the methanol extract of <i>S. aurita</i> twigs for the first time. Additionally, salicin-7-sulfate was present in <i>S. aurita</i> twigs. Procyanidin B-1, taxifolin, trans-p-hydroxycinnamic acid, and catechin showed growth inhibitory activity against <i>B. cereus</i> with a MIC value of 250 µg/mL.