Inactivation of a pathogenic NDM-1-positive Escherichia coli strain and the resistance gene bla <subscript>NDM-1</subscript> by TiO <subscript>2</subscript> /UVA photocatalysis.

Proliferation of bla NDM-1 in water and wastewater is particularly concerning because of multidrug-resistance and horizontal transfer of the gene. In the present study, a pathogenic NDM-1-positive Escherichia coli strain (named E. coli NDM-1) and the bla NDM-1 gene were treated with titanium dioxide (TiO 2 )/ultraviolet A (UVA) photocatalysis. Effects of catalyst dose, UVA intensity, and phosphate on bacteria and intracellular and extracellular bla NDM-1 genes were determined. With increases in TiO 2 dose and UVA intensity, the inactivation rate of E. coli NDM-1 increased greatly in saline solution. However, phosphate in water hindered adsorption of bacteria to TiO 2 and partly changed the TiO 2 photocatalytic pathway, resulting in low degradation efficiency. Although inactivation of E. coli NDM-1 was highly efficient, TiO 2 /UVA photocatalysis had little effect on removal of the bla NDM-1 gene. During the 2-h photocatalytic experiments, E. coli cells decreased by 4.7-log, while the bla NDM-1 gene decreased by 0.7- ~ 1.5-log. Moreover, the degradation rate of extracellular bla NDM-1 was ~2.7 times higher than that of intracellular genes. Abundance and transformation frequency of residual bla NDM-1 genes remained high, even when bacteria were completely inactivated, indicating potential health risks. Increases in treatment time and UVA irradiation intensity are needed to remove the bla NDM-1 gene to sufficiently low levels.

Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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