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Wastewater treatment plants (WWTPs) have been regarded as important point-sources of antibiotic resistance genes (ARGs) in aquatic environments. To investigate the distribution and removal of ARGs in WWTPs, a pharmaceutical wastewater treatment plant (PWWTP) and an integrated wastewater treatment plant (IWWTP) in a fine-chemical industrial park were chosen, and polymerase chain reaction (PCR) and real-time PCR techniques were used to determine the occurrence and abundances of ARGs along the treatment processes. Ten and fifteen ARGs were detected initially in the influents of PWWTP and IWWTP respectively, in which tetracycline and sulfonamide resistance genes were frequently reported, while dfrA13 was first reported in WWTPs. The most abundant ARGs in the influents were sul Ⅰ and sul Ⅱ , followed by dfrA13 , tetQ , floR , tetO , and tetW . The total ARGs increased by 0.21 log after the treatment by PWWTP, whose effluent contributed 0.87% to the inflow yet 5.05% to the total ARGs of IWWTP. Finally the total ARGs removed by IWWTP was 1.03 log, with the remaining ARGs then transported within the final effluent to the nearby coastal area. The authors concluded that the environmental and other impacts from the spread of ARGs on the microbial communities of the coastal environment needed further study.

For revealing the characteristics of antibiotic resistance genes (ARGs) in wastewater treatment systems, real-time PCR was adopted to investigate the variation of abundances of cell-associated ARGs and cell-free ARGs, in a municipal wastewater treatment system (M for short) and a coking wastewater treatment system (C for short). In system M, the absolute abundances of the cell-associated ARGs, sul Ⅱ,tetC,blaPSE-1 , and ermB , were much higher than those of the cell-free fractions in the influent. The biological treatment process did not enrich antibiotic resistance bacteria (ARBs) and membrane filtration of the MBR effectively reduced both cell-associated and cell-free DNA in water. The total ARGs removal was 2.54-4.95 logs. In system C, the biological treatment process enriched the sul Ⅱ -carried ARBs; however, the relative and absolute abundances of cell-free sul Ⅱ were decreased. The succeeding process, coagulation-sand filtration, decreased the absolute abundance of cell-associated sul Ⅱ , but increased the absolute abundance of cell-free sul Ⅱ in water. The proportion of cell-free sul Ⅱ in total sul Ⅱ gene increased from 0.05% in the biological treatment effluent to 1.33% in the sand filtration effluent and further increased to 9.31% after the effluent was kept at 25℃ and at dark for five days. The ratio of cell-free ARGs to total ARGs increased with deep removal of ARBs and lysis of residual cells. The risk of ARG proliferation by cell-free DNA in the effluent needs further evaluation.