The Effect of the Effluent from a Small-Scale Conventional Wastewater Treatment Plant Treating Municipal Wastewater on the Composition and Abundance of the Microbial Community, Antibiotic Resistome, and Pathogens in the Sediment and Water of a Receiving Stream

Kertu Tiirik,Jaak Truu,Marika Truu,Hiie Nõlvak,Margit Kõiv-Vainik,Angela Peeb

doi:10.3390/w13060865

Abstract

The effluents of wastewater treatment plants (WWTPs) are major contributors of nutrients, microbes—including those carrying antibiotic resistance genes (ARGs)—and pathogens to receiving waterbodies. The effect of the effluent of a small-scale activated sludge WWTP treating municipal wastewater on the composition and abundance of the microbial community as well as the antibiotic resistome and pathogens in the sediment and water of the receiving stream and river was studied using metagenome sequencing and a quantitative approach. Elevated Bacteroidetes proportions in the prokaryotic community, heightened sulfonamide and aminoglycoside resistance determinants proportions, and an increase of up to three orders of magnitude of sul1–sul2–aadA–blaOXA2 gene cluster abundances were recorded in stream water and sediments 0.3 km downstream of a WWTP discharge point. Further downstream, a gradual recovery of affected microbial communities along a distance gradient from WWTP was recorded, culminating in the mostly comparable state of river water and sediment parameters 3.7 km downstream of WWTP and stream water and sediments upstream of the WWTP discharge point. Archaea, especially Methanosarcina, Methanothrix, and Methanoregula, formed a substantial proportion of the microbial community of WWTP effluent as well as receiving stream water and sediment, and were linked to the spread of ARGs. Opportunistic environmental-origin pathogens were predominant in WWTP effluent and receiving stream bacterial communities, with Citrobacter freundii proportion being especially elevated in the close vicinity downstream of the WWTP discharge point.

Highlights

Bacterial infections have once again become a threat in modern medicine [1], owing to the rise of resistance to all currently developed antibiotics [2]
Over 33,000 people in the European Union (EU) and 700,000 globally die due to infections caused by antibiotic-resistant bacteria (ARB) [3,4]
The measurements during the main sampling event showed big differences in water characteristics between stream water upstream (SWU) and downstream water samples (Table 1). This effect was especially pronounced in the case of SW0.3, where the water temperature, ORP, and concentrations of SO4 2− and Ptot were considerably higher than in the SWU

Summary

Introduction

Bacterial infections have once again become a threat in modern medicine [1], owing to the rise of resistance to all currently developed antibiotics [2]. Over 33,000 people in the European Union (EU) and 700,000 globally die due to infections caused by antibiotic-resistant bacteria (ARB) [3,4]. The diverse inherent antibiotic resistome in natural environments [5] becomes combined with the resistance caused by high consumption of antibiotics in outpatient healthcare as well as in agriculture [6]. This might cause further resistance recombinations among both harmless and pathogenic bacteria in human-impacted natural environments that could be transferred back to hospital environments [7]. WWTPs vary in their size and treatment capacity, from small WWTPs treating up to 2000 population equivalent (PE)

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