The use of metal nanoparticles (NPs) as antimicrobial
agents has
become a promising alternative to the problem of antibiotic-resistant
bacteria and other applications. Silver nanoparticles (AgNPs) are
well-known as one of the most universal biocide compounds. However,
selenium nanoparticles (SeNPs) recently gained more attention as effective
antimicrobial agents. This study aims to investigate the antibacterial
activity of SeNPs with different surface coatings (BSA-coated, chitosan-coated,
and undefined coating) on the Gram-negativeStenotrophomonas
bentoniticaand the Gram-positiveLysinibacillus
sphaericusin comparison to AgNPs. The tested NPs
had similar properties, including shape (spheres), structure (amorphous),
and size (50–90 nm), but differed in their surface charge.
Chitosan SeNPs exhibited a positive surface charge, while the remaining
NPs assayed had a negative surface charge. We have found that cell
growth and viability of both bacteria were negatively affected in
the presence of the NPs, as indicated by microcalorimetry and flow
cytometry. Specifically, undefined coating SeNPs displayed the highest
percentage values of dead cells for both bacteria (85–91%).
An increase in reactive oxygen species (ROS) production was also detected.
Chitosan-coated and undefined SeNPs caused the highest amount of ROS
(299.7 and 289% over untreated controls) forS. bentoniticaandL. sphaericus, respectively.
Based on DNA degradation levels, undefined-SeNPs were found to be
the most hazardous, causing nearly 80% DNA degradation. Finally, electron
microscopy revealed the ability of the cells to transform the different
SeNP types (amorphous) to crystalline SeNPs (trigonal/monoclinical
Se), which could have environmentally positive implications for bioremediation
purposes and provide a novel green method for the formation of crystalline
SeNPs. The results obtained herein demonstrate the promising potential
of SeNPs for their use in medicine as antimicrobial agents, and we
proposeS. bentoniticaandL. sphaericusas candidates for new bioremediation
strategies and NP synthesis with potential applications in many fields.