Polyethylene microplastics decreased the chlorine disinfection efficacy of antibiotic resistant bacteria and antibiotic resistance genes

The prevalence of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is threatening human health, while the emerging contaminant microplastics (MPs) may pose challenges for water disinfection. This study aims to investigate the effect and possible mechanism of polyethylene microplastics (PE-MPs) on the chlorine disinfection efficacy of ARB and ARGs. Antibiotic resistant Escherichia coli (AR E. coli) and antibiotic resistant Enterococcus faecalis (AR E. faecalis) and their ARGs were chosen to be the targets in the disinfection, attachment, and survival/regrowth experiments, assessed by standard plate count and qPCR methods. The results indicated that PE-MPs hindered the efficacy of chlorine disinfection with a decrease of 0.99-1.88 log for AR E. coli and 0.80-1.69 log for AR E. faecalis. When sufficient nutrition was available, PE-MPs facilitated the survival/regrowth of disinfected ARB by up to 9.5- and 5.9-fold for AR E. coli and AR E. faecalis, respectively. The effects of concentration and sizes of PE-MPs, as well as solution pH and humic acid, were also studied. Furthermore, the presence of PE-MPs decreased the degradation efficacy of ARGs by 11.1-18.6 percentage points. The possible mechanism by which PE-MPs hindered the chlorine disinfection of ARB/ARGs should be the attachment of ARB to PE-MPs that provided shielding from chlorine. This study highlighted the potential threat of MPs on the control of antibiotic resistance in water. Further studies are needed to develop effective techniques to reduce the burden of MPs on disinfection effectiveness.