# Metagenomic insights into the wastewater resistome before and after purification at large‑scale wastewater treatment plants in the Moscow city

## TL;DR

This study analyzed antibiotic resistance genes in wastewater before and after treatment in Moscow, finding that treatment reduces resistance genes, but some remain in the effluent.

## Contribution

The study provides metagenomic insights into the resistome dynamics in large-scale wastewater treatment plants in Moscow.

## Key findings

- Untreated wastewater contained hundreds of antibiotic resistance genes (ARGs) conferring resistance to common antibiotics.
- Treatment reduced the resistome by 3–4 times, with higher removal efficiency for macrolide and tetracycline resistance genes compared to beta-lactamases.
- Multidrug-resistant strains were detected in both influent and treated effluent, with resistome composition influenced by social and environmental factors.

## Abstract

Wastewater treatment plants (WWTPs) are considered to be hotspots for the spread of antibiotic resistance genes (ARGs). We performed a metagenomic analysis of the raw wastewater, activated sludge and treated wastewater from two large WWTPs responsible for the treatment of urban wastewater in Moscow, Russia. In untreated wastewater, several hundred ARGs that could confer resistance to most commonly used classes of antibiotics were found. WWTPs employed a nitrification/denitrification or an anaerobic/anoxic/oxic process and enabled efficient removal of organic matter, nitrogen and phosphorus, as well as fecal microbiota. The resistome constituted about 0.05% of the whole metagenome, and after water treatment its share decreased by 3–4 times. The resistomes were dominated by ARGs encoding resistance to beta-lactams, macrolides, aminoglycosides, tetracyclines, quaternary ammonium compounds, and sulfonamides. ARGs for macrolides and tetracyclines were removed more efficiently than beta-lactamases, especially ampC, the most abundant ARG in the treated effluent. The removal efficiency of particular ARGs was impacted by the treatment technology. Metagenome-assembled genomes of multidrug-resistant strains were assembled both for the influent and the treated effluent. Ccomparison of resistomes from WWTPs in Moscow and around the world suggested that the abundance and content of ARGs depend on social, economic, medical, and environmental factors.