Unveiling the Potential of CuO and Cu2O Nanoparticles against Novel Copper-Resistant Pseudomonas Strains: An In-Depth Comparison

Four novel <i>Pseudomonas</i> strains with record resistance to copper (Cu²⁺) previously isolated from ecologically diverse samples (<i>P. lactis</i> UKR1, <i>P. panacis</i> UKR2, <i>P. veronii</i> UKR3, and <i>P. veronii</i> UKR4) were tested against sonochemically synthesised copper-oxide (I) (Cu₂O) and copper-oxide (II) (CuO) nanoparticles (NPs). Nanomaterials characterisation by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and High-Resolution Transmission Electron Microscopy (HRTEM) confirmed the synthesis of CuO and Cu₂O NPs. CuO NPs exhibited better performance in inhibiting bacterial growth due to their heightened capacity to induce oxidative stress. The greater stability and geometrical shape of CuO NPs were disclosed as important features associated with bacterial cell toxicity. SEM and TEM images confirmed that both NPs caused membrane disruption, altered cell morphology, and pronounced membrane vesiculation, a distinctive feature of bacteria dealing with stressor factors. Finally, Cu₂O and CuO NPs effectively decreased the biofilm-forming ability of the Cu²⁺-resistant UKR strains as well as degraded pre-established biofilm, matching NPs' antimicrobial performance. Despite the similarities in the mechanisms of action revealed by both NPs, distinctive behaviours were also detected for the different species of wild-type <i>Pseudomonas</i> analysed. In summary, these findings underscore the efficacy of nanotechnology-driven strategies for combating metal tolerance in bacteria.