Antibiotic resistance genes of emerging concern in municipal and hospital wastewater from a major Swedish city

The spread of antibiotic resistance among bacterial pathogens is to a large extent mediated by mobile antibiotic resistance genes (ARGs). The prevalence and geographic distribution of several newly discovered ARGs, as well as some clinically important ARGs conferring resistance to last resort antibiotics, are largely unknown. Targeted analysis of wastewater samples could allow estimations of carriage in the population connected to the sewers as well as release to the environment. Here we quantified ARGs conferring resistance to linezolid (optrA and cfr(A)) and colistin (mcr-1,-2,-3,-4 and-5) and the recently discovered gar (aminoglycoside ARG) and sul4 (sulphonamide ARG) in raw hospital and municipal wastewater as well as treated municipal wastewater during five years ina low antibiotic resistance prevalence setting (Gothenburg, Sweden). Additionally, variations in bac-terial composition of the wastewaters characterized by 16S rRNA sequencing were related to the variations of the ARGs in an attempt to reveal if the presence of known or suspected bacterial host taxa could explain the presence of the ARGs in wastewater. The mcr-1, mcr-3, mcr-4, mcr-5, sul4 and gar genes were detected regularly in all types of wastewater samples while optrA and cfr(A) were detected only in hospital wastewater. The most abundant genes were mcr-3 and mcr-5, especially in municipal wastewater. The detection of optrA was restricted to a peak during one year. Most of the ARGs correlated with taxa previously described as bacterial hosts and associ-ated with humans. Although some of the tentative hosts may include bacteria also thriving in wastewater envi-ronments, detection of the ARGs in the wastewaters could reflect their presence in the gut flora of the contributing populations. If so, they could already today or in the near future hinder treatment of bacterial infec-tions in a setting where they currently are rarely targeted/detected during clinical surveillance. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Automated summary

This study investigates the presence and prevalence of antibiotic resistance genes (ARGs) in wastewater samples. The targeted analysis reveals high carriage of ARGs in wastewater, indicating potential release into the environment. The study also explores the relationship between bacterial composition and ARGs, suggesting possible bacterial hosts for these genes. The findings highlight the importance of understanding ARG contamination in wastewater and its potential impact on bacterial infections and treatment.