Minimum concentration of antibiotics in inducing antibiotic resistance in a biofilm type wastewater treatment system

It has been demonstrated that antibiotic resistance could be induced and enriched under high antibiotic concentrations in biological wastewater treatment systems. However, little is available regarding the minimum antibiotic concentrations in inducing antibiotic resistance during wastewater treatment. Herein, the minimum streptomycin concentration in inducing antibiotic resistance in a biofilm type system treating streptomycin bearing wastewater was investigated by using both culture-independent and culture-based approaches. SYBR-Green quantitative PCR, high-throughput quantitative PCR, and metagenomic approach were used to detected antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs). Over a period of 606 days, a COD removal from 88.5% to 92.8% was achieved for the reactor operated under the same organic (not counting streptomycin concentration changes) and ammonium loading rates and increasing streptomycin concentrations (0, 0.1, 1, 5, 25, 50 mg·L-1), while nitrification stopped at streptomycin concentration of 50 mg·L-1. Significant increase of relative abundances of ARGs and MGEs, as well as resistant bacteria ratio was detected at a streptomycin concentration ranging from 1 to 5 mg·L-1 by SYBR-Green quantitative PCR, high-throughput quantitative PCR and culture-based method (p<0.05). Metagenomic sequencing results further confirmed the above findings. The results demonstrated that it is possible to prevent the induction of antibiotic resistance during wastewater treatment by controlling the influent streptomycin concentration below 1 mg·L-1. This work proposed an effective approach for the management of antibiotic production wastewater.