Our main objective was to analyse and study the effects of the synthesized composite based on selenium nanoparticles and carboxymethyl cellulose (Cekol), hereinafter denoted as SeNPs-Cekol. Firstly, physico-chemical properties of SeNPs-Cekol were characterized in greater detail (size of nanoparticles-from 50 to 150 nm; content of selenium-278 ppm; pH of composite-5.4-5.6; density-990-1010 kg/m(3)), together with assessment of its stability. In addition, the toxicity and mutagenicity on prokaryotic and eukaryotic cells was successfully evaluated. All of the tested bacterial strains were isolated from wound swabs of infectious patients (n = 300) and identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). These strains were consequently exposed to SeNPs-Cekol composite. Almost all of the bacterial strains (n = 63) exhibited inhibition zones larger than 5 mm (limit for sensitivity to antibiotics) after the application of the SeNPs-Cekol (300 mu M). Furthermore, in some tested strains (n = 8 for gram positive (G(+)); n = 4 for gram negative (G(-))) even the inhibition zones larger than 12 mm (limit value for very sensitive bacteria to antibiotics) were observed. Overall, the effects of the composite were higher for the G(+) bacteria in comparison with G(-)bacteria, which are generally more resistant to antimicrobial agents, due to their cell wall structure. Further, we found that mutagenicity of the SeNPs-Cekol was found to be negligible. Even, non-target toxicity tests towards eukaryotic cells did not show any significant inhibition of the cells growth compared to the control. Therefore, it can be concluded that SeNPs-Cekol could be considered to have a potential in treatment of bacterial infections.