Spatial ecology of a wastewater network defines the antibiotic resistance genes in downstream receiving waters

Abstract

Wastewater treatment plants (WWTPs) are an effective barrier in the protection of human and environment health around the world, although WWTPs also are suggested to be selectors and-or reservoirs of antibiotic resistance genes (ARGs) before entering the environment. The dogma about WWTPs as “ARG selectors” presumes that biotreatment compartments (e.g., activated sludge; AS) are single densely populated ecosystems with elevated horizontal gene transfer. However, recent work has suggested WWTP biotreatment compartments may be different than previously believed relative to antibiotic resistance (AR) fate, and other process factors, such as bacterial separation and specific waste sources, may be key to ARGs released to the environment. Here we combined 16S rRNA metagenomic sequencing and high-throughput qPCR to characterise microbial communities and ARGs across a wastewater network in Spain that includes both community (i.e., non-clinical urban) and hospital sources. Contrary to expectations, ARGs found in downstream receiving waters were not dominated by AS biosolids (RAS), but more resembled raw wastewater sources. In fact, ARGs and microbial communities in liquid-phase WWTP effluents and RAS were significantly different (Bray–Curtis dissimilarity index = 0.66 ± 0.11), with a consequential fraction of influent ARGs and organisms passing directly through the WWTP with limited association with RAS. Instead, ARGs and organisms in the RAS may be more defined by biosolids separation and biophysical traits, such as flocculation, rather than ARG carriage. This explains why RAS has significantly lower ARG richness (47 ± 4 ARGs) than liquid-phase effluents (104 ± 5 ARGs), and downstream water column (135 ± 4 ARGs) and river sediments (120 ± 5 ARGs) (Tukey's test, p < 0.001). These data suggest RAS and liquid-phase WWTP effluents may reflect two parallel ecosystems with potentially limited ARG exchange. As such, ARG mitigation in WWTPs should more focus on removing bacterial hosts from the liquid phase, AR source reduction, and possibly disinfection to reduce ARG releases to the environment.

Extended spectrum β-lactamase and carbapenemase genes are substantially and sequentially reduced during conveyance and treatment of urban sewage

“…Results across the three countries show that the UWS compartment strongly shapes the resident community profile. Such clear effects of compartment on communities were identified in previous studies across UWS 9,10,14,19 . This is likely due to the distinct environmental conditions in each UWS compartment.…”

“…STP influents often contains sewage not only from domestic origin but also from hospital sources, with contrasting contributions to the total ARG load. Indeed, compared to domestic sewage, hospital sewage has a higher relative load of multiresistant bacteria and genes, especially clinically important β-lactamase genes [7][8][9][10][11] . It is however not clear to what extent sewage collection and treatment can act as barrier for those clinically important ARGs.…”

“…Realizing that UWSs consist of compartments with very different physical-chemical conditions, efforts to describe ARG dynamics have mainly considered one or a few of these compartments at a time, such as the influent, the biological treatment reactor, and the effluent 4,10,12,14 .…”

“…Realizing that UWSs consist of compartments with very different physical-chemical conditions, efforts to describe ARG dynamics have mainly considered one or a few of these compartments at a time, such as the influent, the biological treatment reactor, and the effluent 4,10,12,14 . However, these efforts fail to capture a full picture of UWS and rigorous studies on the occurrence of ARGs across the different compartments are absent, hampering an integrative understanding of the fate of ARGs from raw sewage, through conveyance, treatment processes, and until final discharge.…”

Occurrence and Removal of Antibiotics, Antibiotic-Resistance Genes and Bacterial Communities in Hospital Wastewater

“…In addition, most hospital wastewater is treated by independent hospital wastewater treatment plants (HWWTPs) and then discharged into the water environment or downstream municipal wastewater treatment plants (MWWTPs). In the past few years, many studies have focused on municipal wastewater treatment plants that receive wastewater from hospitals, communities and industry (Lee et al 2017;Quintela-Baluja et al 2019). However, studies focusing on the hospital wastewater treatment process are limited, leaving a gap of knowledge on the occurrence of antibiotics, from the traditional to the last-line antibiotics, and their corresponding ARGs in hospital wastewater treatment protocols.…”