Antibacterial activity of selenium nanoparticles studied by calorimetry, flow cytometry and electron microscopy

Nanoparticles are of growing interest for various applications due to their unique properties, such as elevated surface-to-volume-ratio and variability of material, surface features, and charge. Therefore, they are applied in industry as catalysts and are investigated concerning their feasibility in drug delivery [1]. Moreover, certain metal nanoparticles possess antimicrobial activity and are therefore considered as an alternative to common antibiotics [2]. Especially due to increasing bacterial resistance against common antibiotics and the lack of the development of novel ones, metal nanoparticles attracted interest in biomedical research.
Silver nanoparticles are well-studied concerning their antimicrobial activity and already applied in medicine and household products. However, cellular interaction mechanisms and consequent toxicity are not entirely elucidated. It is proposed, that nanoparticles either interact with the cell membrane via intermolecular interactions, such as charge-charge interactions or penetrate it. Thus, the size and charge of the nanoparticles are the main properties to influence interaction and antimicrobial activity. Once interacting with the cell extra- or intracellularly, nanoparticles release reactive oxygen species and metal ions, which subsequently damage the cell membrane and affect enzymatic activity, consequently leading to cell death. [2]
Besides silver nanoparticles, selenium nanoparticles exhibit prominent antimicrobial activity, without being studied into more detail [3,4]. In our approach, gram-positive (Lysinibacillus sphaericus) and gram-negative (Stenotrophomonas bentonitica) bacterial strains are chosen due to their different cell wall composition and their putatively differing response to the metal nanoparticles. Calorimetric studies of BSA- and Chitosan-coated selenium nanoparticles exhibited a decrease in growth rate of the bacterial model strains, indicating their antimicrobial activity. To further investigate the cytotoxicity, influence of reactive oxygen species and enzymatic activity, the bacterial model strains are incubated with selenium nanoparticles with different surface coatings and charges and studied via fluorescence-based flow cytometry. Furthermore, electron microscopy is performed to characterize interaction mechanisms, to localize the nanoparticles and to elucidate putative metal ion release.

References:

[1] Faraji, A. H. & Wipf, P. Nanoparticles in cellular drug delivery. Bioorganic Med. Chem. 17, 2950–2962 (2009).
[2] Brandelli, A., Ritter, A. C. & Veras, F. F. in Metal Nanoparticles in Pharma 337–363 (Springer International Publishing, 2017). doi:10.1007/978-3-319-63790-7_1
[3] Piacenza, E. et al. Antimicrobial activity of biogenically produced spherical Se-nanomaterials embedded in organic material against Pseudomonas aeruginosa and Staphylococcus aureus strains on hydroxyapatite-coated surfaces. Microb. Biotechnol. 10, 804–818 (2017).
[4] Srivastava, N. & Mukhopadhyay, M. Green synthesis and structural characterization of selenium nanoparticles and assessment of their antimicrobial property. Bioprocess Biosyst. Eng. 38, 1723–1730 (2015).