Ultraviolet reduction of erythromycin and tetracycline resistant heterotrophic bacteria and their resistance genes in municipal wastewater

Antibiotic resistance in wastewater is becoming a major public health concern, but poorly understood about impact of disinfection on antibiotic resistant bacteria and antibiotic resistance genes. The UV disinfection of antibiotic resistant heterotrophic bacteria and their relevant genes in the wastewater of a municipal wastewater treatment plant has been evaluated. Two commonly used antibiotics, erythromycin and tetracycline were selected because of their wide occurrences in regard to the antibiotic resistance problem. After UV treatment at a fluence of 5 mJ cm(-2), the log reductions of heterotrophic bacteria resistant to erythromycin and tetracycline in the wastewater were found to be 1.4 +/- 0.1 and 1.1 +/- 0.1, respectively. The proportion of tetracycline-resistant bacteria (5%) was nearly double of that before UV disinfection (3%). Tetracycline-resistant bacteria exhibited more tolerance to UV irradiation compared to the erythromycin-resistant bacteria (p < 0.05). Gene copy numbers were quantified via qPCR and normalized to the volume of original sample. The total concentrations of erythromycin- and tetracycline-resistance genes were (3.6 +/- 0.2) x 10(5) and (2.5 +/- 0.1) x 10(5) copies L-1, respectively. UV treatment at a fluence of 5 mJ cm(-2) removed the total erythromycin- and tetracycline-resistance genes by 3.0 +/- 0.1 log and 1.9 +/- 0.1 log, respectively. UV treatment was effective in reducing antibiotic resistance in the wastewater. (C) 2013 Elsevier Ltd. All rights reserved.