Electrochemical flow-through disinfection reduces antibiotic resistance genes and horizontal transfer risk across bacterial species

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs), as emerging pollutants, are released into environment, increasing the risk of horizontal gene transfer (HGT). However, a limited number of studies quantified the effects of ARB disinfection on the HGT risk. This study investigated the inactivation of E. coli 10667 (sul) and the release and removal of ARGs using an electrochemical flow-through reactor (EFTR). Furthermore, the transfer frequencies and potential mechanisms of HGT after disinfection were explored using non-resistant E. coli GMCC 13373 as the recipient and E. coli DH5α carrying plasmid RP4 as the donor. A threshold of current density (0.25 mA/cm2) was observed to destroy cells and release intracellular ARGs (iARGs) to increase extracellular ARGs (eARGs) concentration. The further increase in the current density to 1 mA/cm2 resulted in the decline of eARGs concentration due to the higher degradation rate of eARGs than the release rate of iARGs. The performance of ARGs degradation and HGT frequency by EFTR were compared with those of conventional disinfection processes, including chlorination and ultraviolet radiation (UV). A higher ARGs degradation (83.46%) was observed by EFTR compared with that under chlorination (10.23%) and UV (27.07%). Accordingly, EFTR reduced the HGT frequency (0.69) of released ARGs into the recipient (Forward transfer), and the value was lower than that by chlorination (2.69) and UV (1.73). Meanwhile, the surviving injured E. coli 10667 (sul) with increased cell permeability was transferred by plasmid RP4 from the donor (Reverse transfer) with a higher frequency of 0.33 by EFTR compared with that under chlorination (0.26) and UV (0.16). In addition, the sul3 gene was the least resistant to EFTR than sul1 and sul2 gene. These findings provide important insights into the mechanism of HGT between the injured E. coli 10667 (sul) and environmental bacteria. EFTR is a promising disinfection technology for preventing the spread of antibiotic resistance.