Nano-metal oxides naturally attenuate antibiotic resistance in wastewater: Killing antibiotic resistant bacteria by dissolution and decreasing antibiotic tolerance by attachment

Abstract

Increasing discharge of waste nano metal oxides (NMOs) has become an emerging environmental issue. NMOs in wastewater co-occur with antibiotic resistant bacteria (ARB), changing their fate and associated risks in ways that are not yet well understood. In this study, the survival and antibiotic tolerance of ARB in wastewater were examined after exposure to three different NMOs at various retention times. Results indicated that NMOs killed 45.0% ~ 62.0% of ARB and decreased their antibiotic tolerance by 11.0% ~ 58.4%. The toxicity of NMOs was in the order of nZnO > nCuO > nTiO2 and was higher with longer retention times. Both direct attachment and dissolution of ions from NMOs led to their toxicities in wastewater. Notably, dissolution of ions was the main mechanism for ARB death by inducing reactive oxygen species (ROS) and destroying the cell membrane. Whereas, direct attachment was responsible for decreasing the antibiotic tolerance, causing antibiotic resistance gene mutations and modulating stress responses of transcriptome (mostly upregulation). These findings stress the role of NMOs in influencing the threat of antibiotic resistance in wastewater and provide insights for its natural attenuation by NMOs.