Oxidative stress generated at nickel oxide nanoparticle interface results in bacterial membrane damage leading to cell death

Abstract

Metal oxide nanoparticles (NPs) have shown enhanced antibacterial effects against many bacteria. Thus, understanding the potential antibacterial effects of nickel oxide nanoparticles (NiO NPs) against Gram-positive and Gram-negative pathogenic bacteria is an urgent need to enable the exploration of NiO NP use in biomedical sciences. To this end, NiO NPs were synthesized by microwave assisted hydrothermal synthesis method. The synthesized NPs were characterized by X-ray diffraction (XRD) and Fourier Transfer Infrared (FT-IR) and UV-visible spectroscopy. The morphological features of the synthesized NiO NPs were analysed using Transmission Electron Microscopy (TEM) and FE-SEM analysis. The antibacterial activity of NiO NP was explored using different antimicrobial and biophysical studies. The obtained data reveals that the NiO NP has stronger antibacterial activity against Gram-positive bacteria compared to Gram-negative bacteria. The mechanism behind the antibacterial activity of the NiO NP was explored by evaluating the amount of ROS generation at the NiO NP interface. The effect of ROS generation on the bacterial membrane was evaluated by BacLight assay and morphological analysis of the bacterial membrane using FE-SEM. The data altogether suggested that the oxidative stress generated at the NiO NP interface resulted in membrane damage leading to bacterial cell death.

Fig. 1. Characterization of synthesized NiO NP. (a) XRD pattern, (b) FE-SEM images of synthesized NiO NP, (c) EDX analysis and (d) TEM images of NiO NP.

Fig. 2. FT-IR spectra (a), DLS analysis (b), zeta potential measurements (c) and UV-visible absorption spectrum (d) of synthesized NiO NP.

Fig. 3. Growth kinetics of (a) B. subtilis and (b) E. coli in the absence and presence of different concentrations of NiO NP.

Fig. 4. ROS detection of (a) B. subtilis and (b) E. coli in the presence of different concentrations of NiO NP at room temperature.

Fig. 5. Fluorescence microscopic images of B. subtilis (a-i) control, (a-ii) 25 μg mL⁻¹ (a-iii) 500 μg mL⁻¹ of NiO NP and E. coli (b-i) control, (b-ii) 25 μg mL⁻¹, and (b-iii) 500 μg mL⁻¹ of NiO NP.

Fig. 6. Percentage of live and dead cells in the presence of NiO NP, (a) B. subtilis and (b) E. coli.

Fig. 7. FE-SEM analysis of NiO NP treated B. subtilis. (a) Control (without NiO NP treatment), and (b) showing membrane damage in NiO NP treated cells.