Response of antibiotic resistance to the co-existence of chloramphenicol and copper during bio-electrochemical treatment of antibiotic-containing wastewater

Concerns have been raised regarding co-selection for antibiotic resistance among microorganisms exposed to antibiotics and metals. As a promising approach for treating antibiotics and heavy metal-containing wastewater, a bio-electrochemical system (BES) can be used for antibiotic and heavy metal removal. This study determined the fate of antibiotic resistance genes (ARGs) in a BES when exposed to chloramphenicol (CAP) and Cu2+. The ARGs encoding the efflux pump (cmlA, floR, and tetC), the class 1 integron integrase-encoding gene, and the sul1 gene were analyzed. The results indicated that the co-existence of CAP and different concentrations of Cu2+ had significant influence on the relative abundances of the ARGs. The changes in the bacterial community structure and the results of a quantitative correlation analysis between the bacterial community and the ARGs confirmed that the shift in the potential hosts was the key reason for the changes of the ARGs. This study sheds new light on the mechanisms of ARGs variations in BES under the co-selection pressure of antibiotics and heavy metals.