Impacts of coexisting antibiotics, antibacterial residues, and heavy metals on the occurrence of erythromycin resistance genes in urban wastewater

Antibiotic resistance is a global challenge and represents a growing threat on human health worldwide. Wastewater treatment plants (WWTPs) are generally considered as hotspots for control and/or dissemination of antibiotic resistance. The role of antibiotics, antibacterial residues, and heavy metals played on the evolution and spread of antibiotic resistance is still not well understood. Here, the occurrence of antibiotics (i.e., macrolides, tetracyclines, sulfonamides, and quinolones), antibacterial residues (i.e., triclosan), as well as heavy metals (i.e., cadmium, chromium, copper, zinc, lead, and nickel) in urban wastewater was investigated. Also, the abundances of erythromycin resistance genes (ERY-ARGs) including ere (A), ere (B), mef (A)/ mef (E), erm (A), erm (B), erm (C), and msr (A)/ msr (B) genes were screened. A relationship between certain antibiotics, antibacterial residues, and heavy metals and ERY-ARGs was demonstrated. ERY presented significant correlations (0.883 < r < 0.929, P < 0.05) with ere (A), ere (B), and mef (A)/ mef (E) genes, while tetracycline exhibited a significant correlation ( r = 0.829, P < 0.05) with erm (B) genes. It is noteworthy that triclosan correlated significantly (0.859 < r < 0.956, P < 0.05) with ere (A), ere (B), mef (A)/ mef (E), and erm (B) genes. In addition, significantly positive correlations (0.823 < r < 0.871, P < 0.05) were observed between zinc and lead and certain ERY-ARGs (i.e., ere (B), mef (A)/ mef (E), erm (B), etc.). Further investigations should be involved to elucidate the co-selection and/or cross-selection mechanisms due to co-existence of these selective factors in urban wastewater.