Disinfection by-products (DBPs) are one of the unintended consequences of water disinfection that are commonly detected in various water environments. Although DBPs are known to induce antimicrobial resistance via stimulation of chromosomal mutations, it remains unclear whether low-concentration of DBPs could stimulate the conjugative transfer of antibiotic resistance genes (ARGs). The present study aimed to investigate the effect of two typical DBPs, namely trichloromethane (TCM) and dichloroacetonitrile (DCAN), on the conjugative transfer of RP4 plasmid in Escherichia coli genera. The results of the study demonstrated that exposure to low concentrations of TCM and DCAN significantly stimulated conjugative transfer of ARGs, wherein application of 25 μg/L of TCM and 10 μg/L of DCAN resulted in maximum fold change of ~5.5- and ~6.0-fold, respectively, at 16 h of exposure. Further, assessment of underlying mechanisms revealed the involvement of intracellular reactive oxygen species generation, SOS response, increase in cell membrane permeability, upregulation of expression of genes and proteins related to pilus generation, ATP synthesis, and RP4 gene expression. Our findings provided a better understanding of the hidden biological effects and the ecological risks of DBPs in the water environment, especially concerning their effect on the spread of antibiotic resistance.

Currently, due to abuse in the use of human antibiotics and the weak regulatory control that the authorities have over sewage discharge and manure management, antibiotic resistance genes (ARGs) have become a new type of environmental pollutant. Three different natural water bodies (Poyang Lake, Haihe River and Qingdao No.1 Bathing Beach seawater) were sampled during the same periods to conduct a longitudinal comparison of distribution. The distribution and expression of 11 ARGs in 20 species were studied, and the correlations between the expression and the distribution of time and space of the ARGs in different water bodies were also analyzed. With the exception of ermA, blaNDM-1 and vanA, which were not detected in seawater, the other ARGs could be detected in all three water bodies. Tetracycline resistance genes (tetC, tetM and tetQ) in the seawater and Haihe River had even reached 100%, and sulfa ARGs (sul1 and sul2) in the seawater and Poyang Lake, as well as sul2 and sul3 in the Haihe River, had also reached 100%. The ARG pollution in Haihe River was much more serious, since 14 and 17 of 20 ARG species were significantly higher compared with seawater and Poyang Lake, respectively. Some ARGs also had a high absolute abundance. The absolute abundance of macrolide resistance genes (ermB) in seawater was as high as 8.61 × 10⁷ copies/L, and the anti-tuberculosis resistant genes (rpoB and katG) in the Haihe River Basin were highly abundant at 1.32 × 10⁶ copies/L and 1.06 × 10⁷ copies/L, respectively. This indicates that ARGs have gradually become more diverse and extensive in natural water bodies. The results of a redundancy analysis (RDA) of the three water bodies showed that although each water body is affected by different factors in space and time, overall, the presence of AGRs is closely related to the production and life of human beings and the migration of animals.

The presence of disinfection by-products (DBPs) increases the mutagenicity of water and may pose adverse health effects. Gut microbiota exerts a fundamental role on host physiology, and how extrinsic perturbations influence its composition has been increasingly examined. However, the effect of DBPs on gut microbiota is still poorly understood. In the present study, adult zebrafish were exposed to different concentrations of dichloroacetamide (DCAcAm, an emerging nitrogenous DBP) for 30 days. Sequencing of 16S rRNA amplicons revealed a significant change in the richness and diversity of microbiota in the gut of DCAcAm-exposed zebrafish. At the phylum level, the abundance of Proteobacteria decreased and the abundance of Fusobacteria and Firmicutes increased significantly in the gut after exposure to 100 and 500 μg/L DCAcAm. At the genus level, the abundances of several bacteria which are considered pathogens or opportunistic pathogens in fish and closely related to fish metabolism, disease and inflammation (Aeromonas, Stenotrophomonas, Bacteroides and Ralstonia) increased in the DCAcAm-treated groups. Our results reveal that DBPs in drinking water potentially affect gut microbiota composition, which may contribute to the toxicity assessment of DBPs in future and provide new insight into the complex interactions between the DBPs in drinking water and host health.