(521d) Synthesis and Characterization of Biogenic Selenium Nanoparticles Made from Pathogenic Bacteria with Selective Antimicrobial Properties

Antimicrobial Resistance (AMR) to antibiotics has become an urgent crisis for humanity, incurring both medical and economic burden into a continuously growing society. Making matters worse, the future does not offer a relief, as the current overuse and misuse of antibiotics contribute to the rapid development of novel resistant strains of pathogens that we will need to eventually fight. Thus, an alternative, non-resistant-inducing and effective way to treat infection is needed. A perfect candidate comes from the nanoscale and the use of metal-based nanoparticles (MNPs), systems which have long been studied for their antimicrobial properties. However, the cost, efficiency, processing difficulties and ecological safety of traditionally synthesized MNPs prevent their clinical translation. To remedy these challenges, biogenic synthesis of nanoparticles, using living systems (bacteria or fungi, among others), allow for a potentially successful implementation. Among all the possible candidates, selenium nanoparticles (SeNPs) are explored and presented as an alternative antimicrobial agent without the associated resistance problems found in silver nanomaterials.

In this work, SeNPs were synthesized using Escherichia coli (EC), Pseudomonas aeruginosa (PA), Staphylococcus aureus (SA) and Methicillin-resistant Staphylococcus aureus (MRSA), with a diameter of 80-120 nm by culturing bacteria cells in standard conditions and inoculating them with a selenium salt at the end of exponential growth phase. The nanostructures were characterized using Transmission Electron Microscopy (TEM) and Energy Dispersive X-Ray (EDX) to determine the chemical compositions and Fourier transform infrared spectroscopy (FTIR) to validate the chemistry within the samples. Each type of the synthesized SeNPs were tested in antimicrobial studies against the same species that produced them (homogeneous treatment) and other species (heterogeneous treatment) for their ability to inhibit the bacterial growth through optical density measurements and colony forming unit assays. Biocompatibility tests of the SeNPs with human dermal fibroblasts (HDF) were completed, along with resistance studies performed as several rounds of exposure onto pathogens.

Results indicate that SeNPs were successfully generated by all tested strains and exhibited an organic coating layer identified as the protein corona, with unique composition depending on host biofactory. The biogenic SeNPs exhibited antimicrobial properties, with log reduction ranging from 3 – 4 in heterogeneous applications and 5 – 7 in homogeneous applications. Cytotoxicity assays confirmed its safety profile against HDF cells. More significantly, biogenic SeNPs treatment did not induce resistance, in contrast with penicillin and commercialized AgNPs.

These findings confirm the viability of bacteria as a synthesis pathway of SeNPs, and in extension, other metallic NPs. Generated biogenic SeNPs exhibit desired size and antimicrobial properties, with enhanced effectiveness when applied homogeneously. This specificity, along with its limited resistance-inducing property, open the door for biogenic SeNPs to become an easy, safe, cost-effective and potent treatment and a potential solution against the AMR crisis.

Figure: SEM images of MDR-E.coli (A,B) and MRSA (C,D) producing SeNPs, along with TEM images of SeNPs produced by E.coli (E) and S.A (F). Antimicrobial activities of SeNPs produced by E.coli against several pathogens (G) and resistance study (H) demonstrates selectivity and non-resistant-inducing properties