Phenolic Compounds with Antimicrobial Properties in Mushrooms Frequently Encountered in Temperate Deciduous Forests

Mushrooms have long been recognized as a rich source of bioactive compounds, including phenolics, that possess important antioxidant, antimicrobial, and antibacterial properties, including activity against drug-resistant bacteria. This study evaluated total phenolic profile and content, total flavonoids content, the antioxidant activities, antimicrobial and antibacterial activities, of water extracts of edible mushrooms from Romanian deciduous forests, including <i>Cantharellus cibarius</i>, <i>Russula virescens</i>, <i>Lactarius piperatus</i>, and <i>Boletus edulis</i>. The extracts were characterized using high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS) and Fourier Transform Infrared Spectroscopy (FTIR) analysis. Antioxidant activity was determined using DPPH radical-scavenging activity and ABTS radical cation decolorization assay. Antimicrobial and antibacterial activities were tested using standard strains of <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, <i>Pseudomonas aeruginosa</i>, <i>Enterococcus faecalis</i>, and <i>Streptococcus pneumoniae</i> following diffusion testing and time-killing assay, respectively. The HPLC-MS results indicated that major compounds in all the mushrooms belonged to the subclass of hydroxybenzoic acids. Trans-cinnamic acid and hydroxybenzoic acids, particularly gallic acid, 2,3-dihydroxybenzoic acid, and gentisic acid, were the predominant compounds detected in BEE and CCE. Their concentrations were measured as follows: 24 μg/mL, 63 μg/mL, 56 μg/mL, and 14 μg/mL, respectively, for BEE, and 26 μg/mL, 42 μg/mL, 7 μg/mL, and 5 μg/mL, respectively, for CCE. Among phenolic compounds, 2-dihydroxybenzoic acid, 2,3-dihydroxybenzoic acid, <i>p</i>-anisaldehyde, and gentisic acid were positively correlated with both DPPH (45% and 21% inhibition rate for BEE and CCE, respectively) and ABTS (64 and 31% inhibition rate for BEE and CCE, respectively) antioxidant activities. The FTIR analysis revealed the presence of lipids, proteins, and polysaccharides, extracted in different ratios in the water extract. All mushroom extracts showed a dose-dependent response with higher antimicrobial and antibacterial activities at the highest concentration (26.3 µg phenolics BEE, 12.7 µg pphenolics CCE, 28.3 µg phenolics LPE, and 14.5 µg phenolics RVE per well for antimicrobial activity and 175.2 µg phenolics/mL BEE, 84.4 µg phenolics/mL CCE, and 188.9 µg phenolics/mL LPE for antibacterial activity). These species demonstrate potential for the development of alternative antimicrobial formulations, particularly relevant in the context of antibiotic resistance.