Selenium nanoparticles (SeNPs) are increasingly recognized for their exceptional antibacterial properties. This study aimed to develop a green, safe, and efficient method for the biosynthesis of SeNPs using the fungus Eurotium cristatum, a novel approach in SeNP synthesis. The process yielded (36.40 ± 4.22) mg of SeNPs per liter of 1.2 mmol/L sodium selenite supplementation. These SeNPs exhibited an average diameter of 231.7 nm and a negative charge, and they remained stable when stored at 4 ℃. Ultraviolet and visible spectrophotometry revealed a maximum absorption peak at 212 nm, suggesting effective nanoparticle formation. Fourier transform infrared spectrometry indicated that proteins and carbohydrates in the mycelium contributed to the SeNP synthesis. Concentrations of SeNPs below 50 μg Se/mL did not exhibit cytotoxic effects on the growth and proliferation of human hepatocyte L-02 cells. The minimum inhibitory concentration of SeNPs was found to be 2 mg/mL against both methicillin-resistant Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative). The SeNPs compromised the cellular integrity of test strains, causing leakage of intracellular contents and disruption of the oxidative stress system, leading to irreversible damage. Our results demonstrate the potential of SeNPs biosynthesized by E. cristatum to act as effective antibacterial agents, signifying a novel and promising approach to developing natural antimicrobial solutions.

Several of the fungal species associated with Fuzhuan brick tea (FBT) are considered as potential probiotics, but few studies have investigated the probiotic properties of these fungi. Here, we isolated 18 fungal strains from two types of FBT and identified these strains based on internal transcribed spacer (ITS) fragment sequence similarity to reference strains (sequence similarity > 98%). Of the 18 strains, 10 tolerated simulated human digestive conditions for sufficient periods in vitro: pH 2-3, 0.3%-0.5% (m/V) bile salts, and artificial gastrointestinal juices. We then measured the antimicrobial activity of the remaining 10 strains against 5 enteropathogenic bacteria and tested the bacteriostatic effects of the thalli and fermentation broth extracts. Of the 6 strains with strong bacteriostatic effects, we eliminated Eurotium cristatum S-9 due to its low hydrophobicity of (26.12 ± 0.35)%. Finally, 2 exhibited good adhesion abilities to human cells (> 100%). Notably, 2 strains can survive in vivo, because they can be isolated from C57BL/6 mice feces. Thus, 2 strains, Aspergillus cristatus H-1 and A. cristatus H-5, are herein identified as promising candidate probiotic strains. It may be put forward a novel research focus on evaluating potential probiotic fungi from FBT.