Strong Synergistic Antibacterial Effects of Biosynthesized Silver Nanoparticles and Extracts of the Mushroom Lentinus tigrinus

Abstract

The synergistic antibacterial activities of biosynthesized metallic nanoparticles (NPs) and commercial antibiotics are wellknown. However, limited data is available regarding the synergy between metallic NPs and bioactive compounds. This study aimed to synthesize silver nanoparticles (AgNPs) through a green approach using a hot water extract from Tiger Sawgill mushroom, Lentinus tigrinus. The study also aimed to evaluate the antibacterial activity of the biosynthesized AgNPs alone and in combination with an acetone extract of L. tigrinus, known for its antibacterial properties. Characterization of the biosynthesized AgNPs showed that they were monodispersed, spherical particles with an average size of 5–25 nm. They exhibited a face-centered cubic structure and were stable due to the presence of bioorganic coating agents. Fourier transform infrared spectroscopy confirmed that the hot water extract contained reducing and stabilizing biomolecules that facilitated the conversion of Ag+ to Ag0. The microdilution broth assay revealed that the biogenic AgNPs at concentrations lower than 1000 μg/mL were only active against Pseudomonas aeruginosa. However, when combined with the mushroom acetone extract, a synergistic antibacterial effect was observed. This led to a decrease in the lowest effective concentration to 31.25 μg/ mL (p ≤ 0.05). Specifically, the inhibition of Escherichia coli, Staphylococcus aureus, and Bacillus cereus by 500 μg/mL of this mixture increased by 306%, 380%, and 900%, respectively, compared with that of the biosynthesized AgNPs alone (p ≤ 0.05). The present study confirmed that L. tigrinus is a novel source for green biosynthesis of AgNPs with antibacterial properties when combined with the mushroom acetone extract