Treated wastewater irrigation promotes the spread of antibiotic resistance into subsoil pore-water

Abstract

In the present study, we investigated the impact of treated wastewater (TWW) irrigation on the prevalence of antibiotic resistance genes (ARGs) in subsoil pore-water, a so-far under-appreciated matrix. We hypothesized that TWW irrigation increases ARG prevalence in subsoil pore-water. This hypothesis was tested using a multiphase approach, which consisted of sampling percolated subsoil pore-water from lysimeter-wells of a real-scale TWW-irrigated field, operated for commercial farming practices, and controlled, laboratory mesocosms irrigated with freshwater or TWW. We monitored the abundance of six selected ARGs (sul1, blaOXA-58, tetM, qnrS, blaCTX-M-32 and blaTEM), the intI1 gene associated with mobile genetic elements and an indicator for anthropogenic pollution and bacterial abundance (16S rRNA gene) by qPCR. The bacterial load of subsoil pore water was independent of both, irrigation intensity in the field study and irrigation water type in the mesocosms. Among the tested genes in the field study, sul1 and intI1 exhibited constantly higher relative abundances. Their abundance was further positively correlated with increasing irrigation intensity. Controlled mesocosm experiments verified the observed field study results: the relative abundance of several genes, including sul1 and intI1, increased significantly when irrigating with TWW compared to freshwater irrigation. Overall, TWW irrigation promoted the spread of ARGs and intI1 in the subsoil pore-water, while the bacterial load was maintained. The combined results from the real-scale agricultural field and the controlled lab mesocosms indicate that the dissemination of ARGs in various subsurface environments needs to be taken into account during TWW irrigation scenarios.Graphical abstractHighlightsTWW irrigation intensity and sul1 & intI1 abundance correlate in a real-scale fieldARGs & intI1 increase in subsoil pore-water during TWW irrigation in mesocosmsNo increase of ARGs & intI1 in freshwater irrigated mesocosmsTWW irrigation does not affect the bacterial load of subsoil pore-water

Towards risk assessment for antibiotic resistant pathogens in recycled water: a systematic review and summary of research needs

“…Twelve articles were compiled that documented the presence or concentration of specific ARGs targeted via PCR, qPCR, or high‐throughput qPCR (Table 2) (Böckelmann et al ., 2009; Barker‐Reid et al ., 2010; Fahrenfeld et al ., 2013; Elkayam et al ., 2018; Garner et al ., 2018, 2019; Harb et al ., 2019; Marano et al ., 2019; Rocha et al ., 2019; Alygizakis et al ., 2020; Yu et al ., 2020; Kampouris et al ., 2021). The ARGs most frequently targeted for analysis were sul 1 (six articles), bla TEM (five articles), van A (five articles), qnr S (four articles), erm B (three articles), and sul 2 (three articles).…”

“…The compiled studies utilized several different approaches for gaining insight into the potential for horizontal gene transfer. Five studies included monitoring for the class 1 integron integrase gene, int I1 (Garner et al ., 2018, 2019; Harb et al ., 2019; Marano et al ., 2019; Kampouris et al ., 2021), which has been proposed as a monitoring target for antibiotic resistance given the ability of this integron to carry multiple ARGs and its propensity for horizontal gene transfer (Berendonk et al ., 2015; Gillings et al ., 2015). Others used metagenomic sequencing to identify ARGs associated mobile genetic elements, such as plasmids (Garner et al ., 2018).…”

Impact of surface‐applied liquid manure on the drainage resistance profile of an agricultural tile‐drained clay till field

“…In a recent groundwater study, the abundance of tet genes and the intI1 gene was linked to urban pollution (Szekeres et al., 2018). From a wastewater‐irrigated field site, the intI1 exhibited a higher relative abundance than other tested ARGs in the pore water beneath the field and could be correlated to irrigation intensities (Kampouris et al., 2021). In a study from 2015, the intI1 gene was detected in several drainage samples before liquid manure application at the Silstrup field, indicating that intI1 has become part of the natural drainage bacterial ecosystem under standard Danish agricultural practice (Bech et al., 2021).…”

“…Field‐scale studies have examined the leaching of bacteria or selected ARGs in the subsurface, including percolating water, drainage, and groundwater (Kampouris et al., 2021; Luby et al., 2016; Rieke et al., 2018; Wilkes et al., 2019), but a more complete characterization of the leached resistome is still unknown. Recent studies have attempted to develop a more complete description of the resistome in groundwater and surface water (Szekeres et al., 2018; Wu et al., 2020).…”