(198aj) Synthesis and Characterization of Biogenic Selenium Nanoparticles with Antibacterial Properties

Statement of Purpose: Antimicrobial resistance is a global concern that affects to more than 2 million of people each year. Therefore, new approaches to kill bacteria are needed. One of the most promising methodologies may come from metallic nanoparticles since bacteria cannot develop resistance to these nanostructures. While metallic nanoparticle synthesis methods are well studied, they are often accompanied by significant drawbacks such as cost, extreme processing conditions, and toxic waste production. In this work, we explored the environmentally safe synthesis selenium nanoparticles, which have shown promise in killing bacteria.

Methods:UsingEscherichia coli(strain K-12 HB101; Bio-Rad, Hercules, CA), Pseudomonas aeruginosa(Schroeter, Migula, ATCC® 27853™), Staphylococcus aureussubsp. aureus Rosenbach (ATCC® 12600™) and Methicillin-resistant Staphylococcus aureus(MRSA) (F-182, ATCC® 43300™) were used to synthesize biogenic selenium nanoparticles, 90-150 nm selenium nanoparticles were synthesized under standard conditions using an environmentally-safe approach. Bacterial cultures, prepared in Luria-Bertani (LB) media, were inoculated with 2 mM sodium selenite (Na2SeO3) solution to activate the detoxification process that leads to the synthesis of nanoparticles. The nanostructures were characterized using Transmission Electron Microscopy (TEM, JEOL USA Inc., MA), Energy Dispersive X-Ray (EDX) to determine the chemical compositions and Inductively coupled plasma mass spectrometry (ICP-MS) to validate the chemistry within the samples. Nanoparticles were also characterized and tested for their ability to inhibit the bacterial growth through optical density measurements in a SpectraMax M3 spectrophotometer (Molecular Devices, Sunnyvale, CA), and colony forming unit assays. Besides, biocompatibility tests of the nanoparticles with human tissue were accomplished, growing human dermal fibroblast (HDF) cells in media in the presence of biogenic selenium nanoparticles. After an incubation time of 24 hours, the cell growth was analyzed using MTS assay.

Results:It is demonstrated that the bacterial strains used can generate biogenic selenium nanoparticles, concluding that selenium is a thermodynamically favorable metal ion that can be reduced by some reductase enzymes within the cells. TEM images of the nanoparticles showed nanoparticles with a constant distribution size surrounded by cellular debris. The chemistry of the samples was confirmed using EDX analysis, showing the distinct peaks of selenium. The antimicrobial activity of these biogenic selenium nanoparticles was tested against Escherichia coliand Staphylococcus aureusto discover their antibacterial ability. Nanoparticles can produce a decay in

the standard bacterial growth. Besides, the growth of Staphylococcus aureuswas significantly inhibited for those nanoparticles synthesized by Staphylococcus aureus. Colony forming unit assays showed that a bigger concentration of selenium nanoparticle means a better inhibition of the bacterial growth. In vitro cytotoxicity assays were performed with human dermal fibroblasts (HDF) cells. The experiments showed that all nanoparticle concentrations tested did not inhibit the growth of cells while also confirming a high percentage of cell viability. Furthermore, after the incubation period, the growth of the cells was enhanced in comparison with the control without the nanoparticles.

Conclusions: Current and main methods to synthesize selenium nanoparticles use approaches which employ chemical methods. The weakness of these procedures (extreme reaction conditions, production of toxic byproducts, and need of purification) calls for a necessity of alternative approaches. Bacteria can be used to overcome these drawbacks naturally. Therefore, biogenic selenium nanoparticles were synthesized using different bacteria strains through an eco-friendly and green approach. Selenium nanoparticles with small and uniformly shape were synthesized with a relatively homogeneous size distribution. Decay in the bacterial growth was achieved against both Gram positive and Gram negative bacteria, showing no significant cytotoxicity effect when they were cultured with human dermal fibroblasts (HDF) cells.