Variation of antibiotic resistance genes in municipal wastewater treatment plant with A2O-MBR system

The variation of five antibiotic resistance genes (ARGs)—tetG, tetW, tetX, sul1, and intI1—in a full-scale municipal wastewater treatment plant with A2O-MBR system was studied. The concentrations of five resistance genes both in influent and in membrane bioreactor (MBR) effluent decreased as sul1 > intI1 > tetX > tetG > tetW, and an abundance of sul1 was statistically higher than three other tetracycline resistance genes (tetG, tetW, and tetX) (p < 0.05). The concentrations of five ARGs in the influent were all higher in spring (median 105.81–107.32 copies mL−1) than they were in other seasons, and tetW, tetX, and sul1 reached its lowest concentration in autumn (104.61–106.81 copies mL−1). The concentration of ARGs in wastewater decreased in the anaerobic effluent and anoxic effluent, but increased in the aerobic effluent, and then sharply declined in the MBR effluent. The reduction of tetW, intI1, and sul1 was all significantly positively correlated with the reduction of 16S ribosomal DNA (rDNA) in the wastewater treatment process (p < 0.01). The concentration of ARGs (copies mg−1) in sludge samples increased along the treatment process, but the abundance of five ARGs (ratio of ARGs to 16S rDNA) remained the same from anaerobic to anoxic to aerobic basins, while an increment ratio in MBR was observed for all ARGs.