Inactivation of a pathogenic NDM-1-positive Escherichia coli strain and the resistance gene blaNDM-1 by TiO2/UVA photocatalysis.

Proliferation of blaNDM-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 blaNDM-1 gene were treated with titanium dioxide (TiO2)/ultraviolet A (UVA) photocatalysis. Effects of catalyst dose, UVA intensity, and phosphate on bacteria and intracellular and extracellular blaNDM-1 genes were determined. With increases in TiO2 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 TiO2 and partly changed the TiO2 photocatalytic pathway, resulting in low degradation efficiency. Although inactivation of E. coli NDM-1 was highly efficient, TiO2/UVA photocatalysis had little effect on removal of the blaNDM-1 gene. During the 2-h photocatalytic experiments, E. coli cells decreased by 4.7-log, while the blaNDM-1 gene decreased by 0.7- ~ 1.5-log. Moreover, the degradation rate of extracellular blaNDM-1 was ~2.7 times higher than that of intracellular genes. Abundance and transformation frequency of residual blaNDM-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 blaNDM-1 gene to sufficiently low levels.