Antimicrobial resistome in wastewater treatment plants was investigated via shotgun metagenomic analysis over a variety of geographical locations, seasons, and biological treatment configurations. The results revealed that the transition of the antimicrobial resistome occurred at two locations during wastewater treatment, which resulted in a distinctive antimicrobial resistome in influent wastewater, activated sludge, and treated effluent. The antimicrobial resistome in influent wastewater was characterized by a high abundance of antibiotic resistance genes (ARGs) on clinically important drugs, whereas sludge retained a higher abundance of multidrug ARGs associated with efflux pump. Seasonality was the primary factor affecting antimicrobial resistome in influent wastewater, which partially succeeded to the subsequent resistome of activated sludge and treated effluent. Importantly, some ARGs on clinically important drugs in influent wastewater passed through the biological treatment to be discharged in the treated effluent, except in the membrane bioreactor process.

Wastewater is the major source of the emergence of antimicrobial resistance (AMR) in water environment. Wastewater treatment plants (WWTPs) are the important barriers for preventing the spread of AMR in wastewater into water environment, as well as the reservoir of AMR, which can be potentially discharged into treatment effluent. In this study, the antimicrobial resistome in WWTP was investigated using systematic sampling and shotgun metagenomic analysis over a variety of geographical locations, seasons, and biological treatment configurations. The results revealed that the transition of antimicrobial resistome occurred at two locations during the course of wastewater treatment process to develop the distinctive antimicrobial resistome in influent wastewater, activated sludge, and treatment effluent regardless of the geographical locations of WWTPs. The antimicrobial resistome in influent wastewater was characterized by higher abundance of antibiotic resistance genes (ARGs) resistant to clinically important drug classes, whereas sludge retained a higher abundance of multidrug ARGs associated with efflux pump. Seasonality was the primary factor to characterize the antimicrobial resistome in influent wastewater, which was partially succeeded to the subsequent resistome of activated sludge and treatment effluent. Importantly, antimicrobial resistome in the treatment effluent was dependent on process configuration of sludge separation. With conventional final sedimentation, antimicrobial resistome in the treatment effluent was partially affected by the resistome in influent wastewater, suggesting some ARGs in influent wastewater bypassed biological treatment and final sedimentation to be retained in the treatment effluent. On the contrary, the resistome of MBR effluent was independent from wastewater resistome, suggesting good reduction of ARG to clinically important drugs originated from influent wastewater.

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There is considerable concern regarding antibiotic resistance in the water environment due to antibiotic residues from anthropogenic origins. The low antibiotic concentration in the water environment may promote the selection of antibiotic resistance. However, it is unclear how environmental factors affect resistance selection. We investigated the proliferation of quinolone-susceptible faecal bacteria (E. coli) exposed to low norfloxacin concentration (ng/L) at variable temperatures, exposure times, and carbon concentrations, simulating the conditions of the water environment. The induction of antibiotic resistance in thirteen E. coli isolates was more likely to occur at 37 °C. However, resistance also occurred at temperatures as low as 25 °C, provided a longer exposure time of 5 days. These results suggest that antibiotic resistance is more likely to be induced in regions where temperatures may reach 25–37 °C, such as tropical regions.