Bacterial lineages putatively associated with the dissemination of antibiotic resistance genes in a full-scale urban wastewater treatment plant

Carlos Narciso-Da-Rocha,Jaqueline Rocha,Ivone Vaz-Moreira,Felipe Lira,Javier Tamames,Isabel Henriques,José Luis Martinez,Célia M Manaia

doi:10.1016/j.envint.2018.05.040

Abstract

Urban wastewater treatment plants (UWTPs) are reservoirs of antibiotic resistance. Wastewater treatment changes the bacterial community and inevitably impacts the fate of antibiotic resistant bacteria and antibiotic resistance genes (ARGs). Some bacterial groups are major carriers of ARGs and hence, their elimination during wastewater treatment may contribute to increasing resistance removal efficiency. This study, conducted at a full-scale UWTP, evaluated variations in the bacterial community and ARGs loads and explored possible associations among them. With that aim, the bacterial community composition (16S rRNA gene Illumina sequencing) and ARGs abundance (real-time PCR) were characterized in samples of raw wastewater (RWW), secondary effluent (sTWW), after UV disinfection (tTWW), and after a period of 3 days storage to monitoring possible bacterial regrowth (tTWW-RE). Culturable enterobacteria were also enumerated.Secondary treatment was associated with the most dramatic bacterial community variations and coincided with reductions of ~2 log-units in the ARGs abundance. In contrast, no significant changes in the bacterial community composition and ARGs abundance were observed after UV disinfection of sTWW. Nevertheless, after UV treatment, viability losses were indicated ~2 log-units reductions of culturable enterobacteria. The analysed ARGs (qnrS, blaCTX-M, blaOXA-A, blaTEM, blaSHV, sul1, sul2, and intI1) were strongly correlated with taxa more abundant in RWW than in the other types of water, and which associated with humans and animals, such as members of the families Campylobacteraceae, Comamonadaceae, Aeromonadaceae, Moraxellaceae, and Bacteroidaceae.Further knowledge of the dynamics of the bacterial community during wastewater treatment and its relationship with ARGs variations may contribute with information useful for wastewater treatment optimization, aiming at a more effective resistance control.

Highlights

Domestic wastewater has been considered a potential source for the spread of antibiotic resistant bacteria (ARB) (Varela and Manaia, 2013; Berendonk et al, 2015; Manaia et al, 2016; Sharma et al, 2016; Huijbers et al, 2015)
Secondary treatment was associated with important variations in the relative abundance of different bacterial classes (Fig. 1A)
With the increase on the relative abundance of members of the classes Alphaproteobacteria, TM7-1 and ZB2 (Fig. 1B) and the simultaneous decrease of the classes Epsilon258 and Gammaproteobacteria, and of Bacteroidia and Clostridia (Fig. 1B). Considering the classes that represented more than 5% of the total bacterial community in each sample, significant composition variations after UV disinfection were only observed for Alphaproteobacteria that increased 2.3%

Summary

Introduction

Domestic wastewater has been considered a potential source for the spread of antibiotic resistant bacteria (ARB) (Varela and Manaia, 2013; Berendonk et al, 2015; Manaia et al, 2016; Sharma et al, 2016; Huijbers et al, 2015). The unveiling of potential associations between ARGs and bacterial lineages will be a valuable contribution for better understanding the ecology of antibiotic resistance The enrichment of this kind of knowledge, based on multiple studies conducted in distinct types of wastewater treatment and worldwide, may contribute to defining general patterns of ARGs71 bacterial phylogeny associations, with positive implications on antibiotic resistance control. This was the major motivation for this study, conducted at a full-scale urban wastewater treatment plant (UWTP)

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