Abstract
Chlorine disinfection to drinking water plays an important role in preventing and controlling waterborne disease outbreaks globally. Nevertheless, little is known about why it enriches the antibiotic resistance genes (ARGs) in bacteria after chlorination. Here, ARGs released from killed antibiotic-resistant bacteria (ARB), and culturable chlorine-injured bacteria produced in the chlorination process as the recipient, were investigated to determine their contribution to the horizontal transfer of ARGs during disinfection treatment. We discovered Escherichia coli, Salmonella aberdeen, Pseudomonas aeruginosa and Enterococcus faecalis showed diverse resistance to sodium hypochlorite, and transferable RP4 could be released from killed sensitive donor consistently. Meanwhile, the survival of chlorine-tolerant injured bacteria with enhanced cell membrane permeabilisation and a strong oxidative stress-response demonstrated that a physiologically competent cell could be transferred by RP4 with an improved transformation frequency of up to 550 times compared with the corresponding untreated bacteria. Furthermore, the water quality factors involving chemical oxygen demand (CODMn), ammonium nitrogen and metal ions (Ca2+ and K+) could significantly promote above transformation frequency of released RP4 into injured E. faecalis. Our findings demonstrated that the chlorination process promoted the horizontal transfer of plasmids by natural transformation, which resulted in the exchange of ARGs across bacterial genera and the emergence of new ARB, as well as the transfer of chlorine-injured opportunistic pathogen from non-ARB to ARB. Considering that the transfer elements were quite resistant to degradation through disinfection, this situation poses a potential risk to public health.
Highlights
Antibiotic resistance has become a worldwide crisis
antibiotic-resistant bacteria (ARB) presented diverse resistance to chlorine disinfection during NaClO exposure To observe the dynamics of ARB killing, the inactivation kinetics of four kinds of ARB—E. coli, P. aeruginosa, Table 1 Transformability of released RP4 from NaClOtreated ARB (105 − 106cfu/mL) to chemically competent Escherichia coli DH5α at pH 7.2, 20 °C
This study is the first to find that chlorine disinfection, which has been used to eliminate pathogens and improve public health in past years [35], increased the frequency of natural transformation and inevitably promoted the horizontal transfer of antibiotic resistance genes (ARGs) across bacterial genera via culturable chlorine-injured bacteria
Summary
Antibiotic resistance has become a worldwide crisis. It is estimated that antibiotic resistance will cause as many as 10. We showed that cultivated chlorine-tolerant injured non-ARB, which was a kind of competent cell with cell membrane permeabilisation and a strong oxidative stress-response, could uptake released RP4 from sensitive donors and shift into ARB persistently with a higher frequency. This information will help in comprehending the reasons for the enrichment of the ARG level during the chlorination process and reveal the dissemination approaches of ARGs between bacteria during the disinfection process
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