| In recent years, antibiotics were detected frequently in various environment media, which promoted the occurrence of resistant bacteria and antibiotic resistance genes. Antibiotic resistance genes (ARGs) were discharged into the environment by animals, hospitals and sewage treatment plant effluent, and migrated in different regions or species, which posed a potential threat to public health and safety. More and more attention has been paid to the environmental behavioral effects of ARGs, and the removal process has also become a pressing problem.To explore the relationship between antibiotic resistant bacteria and resistance genes pollution levels, high performance liquid chromatography-mass spectrometry (HPLC-MS), colony counting method, and real-time quantitative polymerase chain reaction (qPCR) were applied to analyze the levels of antibiotics, resistant bacteria and ARGs in surface water, groundwater and sediment samples, respectively, from Wangyanggou River. The aqueous samples were unavoidably contaminated with antibiotics, and the target antibiotics present in high levels were oxytetracycline, tetracycline, chlortetracycline, ofloxacin, sulfamethoxazole, and trimethoprim, with maximum concentrations of the individual contaminant at3.6×105,9.7×103,6.9×104,1.2×104,4.8×103, and1.1×103ng/L, respectively. Oxytetracycline, tetracycline, ciprofloxacin and roxithromycin were the most frequently detected compounds in sediment samples, with maximum concentrations of the individual contaminant at1.6×105,1.7×104,2.1×103and2.5×103ng/g, respectively. The results also revealed that the high intensity of aquaculture activities could contribute to the increasing levels of antibiotics in the area. According to the ratios of measured environmental concentration (MEC) to predicted no-effect concentration (PNEC), chlortetracycline, tetracycline, ofloxacin, ciprofloxacin, erythromycin-H2O and sulfamethoxazole may present possible environmental risk to the individual aqueous species. The number of tetracycline andsulfonamide resistance bacteria was4.00×101to2.13×104CFU/mL and6.67X101to7.34×105CFU/mL, respectively, and the count of resistant bacteria in water was3to4orders of magnitude lower than that in sediments. The abundance of five tetracycline resistance genes(tetA, tetB, tetE, tetW and tetZ), two sulfonamide (sull, sul2) resistance genes and two integron genes (intl, int2) detected were relatively higher in all samples.The two genes, tetA and sull were dominant resistance genes with the relative abundance above1.58×10-2in Wangyanggou River. Principal component analysis indicated that the abundance of ARGs may be affected by different pollution sources and complicated water quality characteristics. It can be seen from the phylogenetic analysis of tet(B) that the water quality change would result in the diversity of resistant strains.In this study, the abundance and distribution of antibiotics and ARGs from a sewage treatment plant (STP) and its effluent-receiving river in Beijing China were characterized. Three classes of antibiotics including tetracycline, sulfonamide and quinolone were quantified. In the secondary effluent they were detected at195,2001and3866ng/L, respectively, which were higher than in the receiving river water. A total of13ARGs (6tet genes:tetA, tetB, tetE, tetW, tetM and tetZ,3sulfonamide genes:sul1, sul2and sul3, and4quinolone genes:gryA, parC, qnrC and qnrD) were determined by quantitative PCR. For all ARGs, sulfonamide resistance genes were present at relatively high concentrations in all samples, with the highest ARG concentration above10-1. ARGs remained relatively stable along each sewage treatment process. The abundances of detected ARGs from the STP were also higher than its receiving river. Bivariate correlation analysis showed that relative tet gene copies (te/B/16SrRNA and tet W/16SrRNA) were strongly correlated with the concentrations of tetracycline residues (r2>0.8, p<0.05), while no significant correlations occurred between sulfonamides and sul genes. A negative correlation between the relative abundance of quinolone resistance gene (anrC/16S rRNA) and the concentrations of enrofloxacin (ENR) was also determined. The difference of ARGs levels in the raw influent and secondary effluent suggested that the STP treatment process may induce to increase the abundance of resistance genes. The results showed that the sewage was an important repository of the resistance genes, which need to be effectively treated before discharge into the natural water body. |
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