Effect of Nanosilver and Antibiotic Loading on Fate of Antibiotic Resistance Genes in Thermophilic and Mesophilic Anaerobic Digesters

摘要

Wastewater treatment plants (WWTPs) have been identified as vehicles for the conveyance ofpharmaceuticals and nanosilver contaminants as well as antibiotic resistant bacteria (ARB) andantibiotic resistance genes (ARGs) from anthropogenic sources to the environment. Additionally,WWTPs have high nutrient loadings, dense microbial populations, and trace antibioticconcentrations that create “breeding ground” conditions for the selection, transfer anddissemination of ARGs among various bacteria. The use of nanosilver in consumer products ison the rise because of its antimicrobial properties and, as such, nanosilver may incur a selectivepressure similar to antibiotics.The purpose of our studies was to investigate the fate of ARGs in mesophilic and thermophilicanaerobic digestion under conditions of artificially-applied antibiotic and nanosilver selectionpressures, possible co-selection of multiple ARGs via integrons, and the impact of nanosilverand antibiotic loading on thermophilic anaerobic digestion performance.This study suggests that anaerobic digestion is an effectively reduces ARG loading to theenvironment up to one or two orders of magnitude even in the presence of contaminant selectionpressures. The fact that ARG reductions remained consistent in spite of the application ofselection pressures suggest that the digester operating conditions themselves are the major factorthat governs the composition of the bacterial community and thus the prevalence of ARGs. Inaddition, this work did not find any impact of nanosilver at environmentally relevantconcentrations (0.01 to 1.0 mg/L; ~0.7 to 70 mg-Ag/kg TS) on thermophilic anaerobic digestion.