Impacts of reclaimed water irrigation on soil antibiotic resistome in urban parks of Victoria, Australia

Abstract

a b s t r a c tThe effluents from wastewater treatment plants have been recognized as a significant environmental reservoir of antibiotics and antibiotic resistance genes (ARGs). Reclaimed water irrigation (RWI) is increasingly used as a practical solution for combating water scarcity in arid and semiarid regions, however, impacts of RWI on the patterns of ARGs and the soil bacterial community remain unclear. Here, we used high-throughput quantitative PCR and terminal restriction fragment length polymorphism techniques to compare the diversity, abundance and composition of a broad-spectrum of ARGs and total bacteria in 12 urban parks with and without RWI in Victoria, Australia. A total of 40 unique ARGs were detected across all park soils, with genes conferring resistance to b-lactam being the most prevalent ARG type. The total numbers and the fold changes of the detected ARGs were significantly increased by RWI, and marked shifts in ARG patterns were also observed in urban parks with RWI compared to those without RWI. The changes in ARG patterns were paralleled by a significant effect of RWI on the bacterial community structure and a co-occurrence pattern of the detected ARG types. There were significant and positive correlations between the fold changes of the integrase intI1 gene and two b-lactam resistance genes (KPC and IMP-2 groups), but no significant impacts of RWI on the abundances of intI1 and the transposase tnpA gene were found, indicating that RWI did not improve the potential for horizontal gene transfer of soil ARGs. Taken together, our findings suggested that irrigation of urban parks with reclaimed water could influence the abundance, diversity, and compositions of a wide variety of soil ARGs of clinical relevance. One-sentence summary: Irrigation of urban parks with treated wastewater significantly increased the abundance and diversity of various antibiotic resistance genes, but did not significantly enhance their potential for horizontal gene transfer.

Review of Antimicrobial Resistance in the Environment and Its Relevance to Environmental Regulators

“…The prospect of less reliable water sources into the future, as a result of a changing climate, might make this source of water more important in the UK (Prudhomme et al, 2012). Reclaimed water is currently used to sprinkler irrigate crops (e.g., lettuce, carrots, and green beans), golf courses, and landscapes (Kinney et al, 2006; Calderón-Preciado et al, 2013; Thanner et al, 2016), and as such is being introduced into soil habitats that might have previously been unexposed to significant quantities of ARGs or resistance-driving chemicals (Fahrenfeld et al, 2013; Han et al, 2016). The amplification of antibiotic resistant bacteria within distribution system for reclaimed water is poorly understood, but poses a potential risk to humans and the environment (Fahrenfeld et al, 2013).…”

Diversity of herbaceous plants and bacterial communities regulates soil resistome across forest biomes

“…S10. Comparison of the diversity and relative abundance of ARGs in the forest ecosystems in this study and some human-impacted soils including 85 coppercontaminated soils (Hu et al, 2016), 85 nickelcontaminated soils , 30 animal manureamended soils and 50 antibioticstreated soils by using the same HT-qPCR array.…”

“…Soil is one of the largest environmental reservoir comprising approximately 30% of known ARGs in public repositories (Forsberg et al, 2012;, and is one of the most complex ecosystems in terms of ecological niches and biodiversity . To date, a large body of studies have documented the prevalence of ARGs in environments under anthropogenic perturbations, such as soils with manure amendments (Zhu et al, 2013;Zhang et al, 2017), contaminated with pharmaceutical residues or heavy metals and irrigated with reclaimed water (Wang et al, 2014;Han et al, 2016). We have, however, limited knowledge of the background levels of antibiotic resistance and the distribution of ARGs in natural settings with little or no human disturbance.…”

Lateral gene transfer, bacterial genome evolution, and the Anthropocene

“…Release of wastewater into the environment disseminates antibiotic resistance genes and mobile elements throughout the natural world . In this manner, antibiotic resistance genes spread into freshwater ecosystems, soils, and wild animals . This phenomenon is now so pervasive that mobile genetic elements associated with resistance phenotypes have been proposed as a general proxy for anthropogenic pollution .…”