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

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