Antibacterial properties and mechanism of selenium nanoparticles synthesized by Providencia sp. DCX.

Selenium nanoparticles (SeNPs) have attracted great interest as a potential antimicrobial agent. However, there is limited research on the antibacterial activity and possible mechanisms of biosynthesized SeNPs. In this study, spherical bio-SeNPs with an average size of 120 nm were synthesized by strain Providencia sp. DCX. The SeNPs were further applied to investigate the antibacterial properties of model bacteria, including Gram-positive (Staphylococcus aureus, Bacillus cereus and Bacillus subtilis) and Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli and Vibrio parahemolyticus). The biosynthesized SeNPs demonstrated strong inhibition activity against the growth of these pathogens. When treated with 500 mg/L SeNPs, most of the tested bacteria were destructed within 12 h, among which the mortality rates of Gram-negative bacteria were much better. The leakage tests illustrated that there existed more proteins and polysaccharides outside the cells after reacted with bio-SeNPs. It was indicated that the leakages of proteins and polysaccharides were caused by permeability changes of membranes and the disruption of cell walls. And the change of reactive oxygen species (ROS) intensity indicated that oxidative damage may play the significant role in the antibacterial processes. The results showed that several bacteria could be effectively inhibited and destructed, suggesting the potential of using the biosynthesized SeNPs as antibacterial agents for bacterial infectious diseases.