Role of wastewater treatment plants on environmental abundance of Antimicrobial Resistance Genes in Chilean rivers

BACKGROUND: Point sources such as wastewater treatment plants (WWTPs) commonly discharge their effluent into rivers. Their waste may include antibiotic residues, disinfectants, antibiotic resistant bacteria (ARB), and Antimicrobial Resistance Genes (ARG). There is evidence that ARG can be found in the natural environment, but attribution to specific point sources is lacking.

OBJECTIVES: The goal of this study was to assess the release and dissemination of ARG from three WWTPs in southern Chile via two pathways: through the river systems, and through wild birds.

METHODS: A longitudinal study was conducted, collecting river sediment samples at different distances both upstream and downstream from each WWTP. Wild birds were sampled from around one of the WWTPs once a month for 13 months. A microfluidic q-PCR approach was used to quantify 48 genes covering different molecular mechanisms of resistance, and data was analyzed using ordination methods and linear mixed regression models.

RESULTS: There was a statistically significant increase downstream from the WWTPs (p < 0.05) for 17 ARG, but the downstream dissemination through the rivers was not clear. Beta-lactamase genes bla KPC, bla TEM, and bla SHV were the most abundant in birds, with higher abundance of bla SHV in migratory species compared to resident species (p < 0.05). The gene profile was more similar between the migratory and resident bird groups compared to the WWTP gene profile.

CONCLUSIONS: While results from this study indicate an influence of WWTPs on ARG abundance in the rivers, the biological significance of this increase and the extent of the WWTPs influence are unclear. In addition, wild birds were found to play a role in disseminating ARG, although association to the specific WWTP could not be ascertained.