Mechanistic study of copper oxide, zinc oxide, cadmium oxide, and silver nanoparticles-mediated toxicity on the probiotic .

The use of metal/metal oxide nanoparticles (NPs) in consumer products has increased dramatically. Accordingly, human exposure to these NPs has increased. , a member of the beneficial gut microbiota, is essential for human health. In the present study, the toxic effect of three metal oxides (CuO, ZnO, and CdO) and one metal (Ag) NPs on were investigated in vitro. was susceptible to all the prepared NPs in a dose-dependent manner, visualized as an increase in the zones of inhibition and a significant reduction in the maximum specific growth rates (). The minimal inhibitory concentrations were 5.8, 26, 560, and 560 µg/mL for CdO-, Ag-, ZnO-, and CuO-NPs, respectively, and the respective minimal bactericidal concentrations were 60, 70, 1500, and 1500 µg/mL. Electron microscopic examinations revealed the adsorption of the prepared NPs on cell surface, causing cell wall disruption and morphological changes. These changes were accompanied by significant leakage of cellular protein content by 214%, 191%, 112%, and 101% versus the untreated control when was treated with CdO-, Ag-, CuO-, and ZnO-NPs, respectively. NPs also induced oxidative damage, where the malondialdehyde level was significantly increased, and glutathione content was significantly decreased. Quantifying the DNA damage using comet assay showed that CuONPs had the maximum DNA tail length (8.2 px vs. 2.1 px for the control). While CdONPs showed the maximum percentage of DNA in tail (15.5% vs. 3.1%). This study provides a mechanistic evaluation of the NPs-mediated toxicity to a beneficial microorganism.