Decreased Efficiency of Free Naked DNA Transformation by Chlorine and UV Disinfection and Its Detection Limitations

Abstract

Antibiotic resistance genes can be spread via gene horizontal transfer (GHT). Chlorination and UV irradiation are common disinfection methods used in wastewater treatment plants before the discharge of treated wastewater. This study aimed to elucidate the effects of disinfection on the transformation of naked DNA in the aquatic environment. The pUC19 plasmid possessing ampicillin-resistant beta-lactamase and subjected to different dosages of chlorine or UV irradiation was used for transformation in Escherichia coli to estimate the transformation efficiency and GHT in the environment after disinfection. The results showed that doses > 0.5 mg-Cl2/L can effectively decrease transformation efficiency (1.21 to 8.83-log10) based on pUC19 as the positive control. UV irradiation can decrease the efficiency (2.37 to 3.39-log10) following 10–60 min of treatment. PCR and qPCR detection have limitations for determining transformation efficiency because they provide approximate estimates damaged DNAs. Overall, these results indicate that proper disinfection management using chlorine and/or UV for treated wastewater before discharge from wastewater treatment plants can prevent the spread of antibiotic resistant bacteria and genes, by decreasing the efficiency of naturally occurring bacterial transformations in wastewater treatment plants.