Correlation of tetracycline and sulfonamide antibiotics with corresponding resistance genes and resistant bacteria in a conventional municipal wastewater treatment plant

Antibiotics and corresponding resistance genes and resistant bacteria have been considered as emerging pollutants worldwide. Wastewater treatment plants (WWTPs) are potential reservoirs contributing to the evolution and spread of antibiotic resistance. In this study, total concentrations of tetracycline and sulfonamide antibiotics in final effluent were detected at 652.6 and 261.1 ng/L, respectively, and in treated sludge, concentrations were at 1150.0 and 76.0 μg/kg dry weight (dw), respectively. The quantities of antibiotic resistance genes and antibiotic resistant bacteria in final effluent were quantified in the range of 9.12 × 105–1.05 × 106 gene abundances /100 mL (genomic copies/100 mL) and 1.05 × 101–3.09 × 103 CFU/mL, respectively. In treated sludge, they were quantified at concentrations of 1.00 × 108–1.78 × 109 gene abandances/100 mL and 7.08 × 106–1.91 × 108 CFU/100 mL, respectively. Significant reductions (2–3 logs, p < 0.05) of antibiotic resistance genes and antibiotic resistant bacteria were observed between raw influent and final effluent. The gene abundances of tetO and tetW normalized to that of 16S rRNA genes indicated an apparent decrease as compared to sulI genes, which remained stable along each treatment stage. Significant correlations (R2 = 0.75–0.83, p < 0.05) between numbers of resistant bacteria and antibiotic concentrations were observed in raw influent and final effluent. No significance (R2 = 0.15, p > 0.05) was found between tet genes (tetO and tetW) with concentration of tetracyclines identified in wastewater, while a significant correlation (R2 = 0.97, p < 0.05) was observed for sulI gene and total concentration of sulfonamides. Correlations of the quantities of antibiotic resistance genes and antibiotic resistant bacteria with corresponding concentrations of antibiotics in sludge samples were found to be considerably weak (R2 = 0.003–0.07).