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Selenium nanocomposites have attracted considerable attention in terms of their antimicrobial activity. It was shown that SeNPs inhibited growth of a variety of bacteria such as Pseudomonas aeruginosa, Streptococcus aureus, and Streptococcus pyogenes in concentration of 100 μg ml⁻¹, but Escherichia coli was of 250 μg ml⁻¹. Moreover, it was found that SeNPs at concentrations of 500 μg ml⁻¹ inhibit growth of pathogenic fungi like Aspergillus clavatus (Srivastava and Mukhopadhyay 2015). In another study, it was found that SeNPs synthesized with Enterococcus faecalis can be effectively used to prevent and treat infections caused by S. aureus (Shoeibi and Mashreghi 2017).

It was demonstrated that antimicrobial activity of SeNPs depends on the method of their synthesis and also on their size. It was found that SeNPs synthesized by the biological (green synthesis) methods usually have greater antimicrobial activity compared to chemically synthesized nanoparticles (Cremonini et al. 2016; Piacenza et al. 2017). Selenium nanocomposites synthesized using Aspergillus orayzae with average size of 55 nm were found to be effective against Acinetobacter calcoaceticus, S. aureus, and Candida albicans (Mosallam et al. 2018). Similarly, SeNPs synthesized using gram‐negative (Stenotrophomonas maltophilia) and gram‐positive (Bacillus mycoides) bacteria were reported active at low minimal inhibitory concentrations (MICs) against P. aeruginosa clinical isolates, but they did not inhibit clinical fungi isolates such as C. albicans and Candida parapsilosis. These biogenic nanocomposites demonstrated a stronger antimicrobial effect than synthetic SeNPs (Cremonini et al. 2016, 2018). SeNPs stabilized with polyvinyl alcohol showed strong growth inhibition against S. aureus at a concentration of 1 ppm, but they did not inhibit growth of E. coli (Tran et al. 2016). Lara et al. (2018) demonstrated the antifungal effect of SeNPs and chitosan against C. albicans.

Moreover, SeNPs obtained through laser ablation in water have MIC of 50 ppm in case of E. coli and S. aureus. However, minimum bactericidal concentration (MBC) toward E. coli and S. aureus was found to be 107 ± 12 and 79 ± 4 ppm, respectively (Guisbiers et al. 2016), but for C. albicans MIC was recorded as 25 ppm (Guisbiers et al. 2017). Using electron microscopy, it was observed that SeNPs can easily stick to the biofilm and then penetrate into the pathogen and damage their cellular structure, replacing sulfur (Guisbiers et al. 2017). Therefore, it is strongly believed that selenium can be promisingly used as an effective antibacterial drug including multidrug‐resistant organisms (Shurygina et al. 2011, 2015,b, 2016; Fadeeva et al. 2015).