Bacterial Genes Encoding Resistance Against Antibiotics and Metals in Well-Maintained Drinking Water Distribution Systems in Finland.

Ananda Tiwari,Ilkka T Miettinen,Tarja Pitkänen,Sallamaari Siponen,Anna-Maria Hokajärvi,Ari Kauppinen,Vicente Gomez-Alvarez,Eila Torvinen,Anniina Sarekoski

doi:10.3389/fmicb.2021.803094

Abstract

Information on the co-occurrence of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) among bacterial communities in drinking water distribution systems (DWDSs) is scarce. This study characterized ARGs and MRGs in five well-maintained DWDSs in Finland. The studied DWDSs had different raw water sources and treatment methods. Two of the waterworks employed artificially recharged groundwater (ARGW) and used no disinfection in the treatment process. The other three waterworks (two surface and one groundwater source) used UV light and chlorine during the treatment process. Ten bulk water samples (two from each DWDS) were collected, and environmental DNA was extracted and then sequenced using the Illumina HiSeq platform for high-throughput shotgun metagenome sequencing. A total of 430 ARGs were characterized among all samples with the highest diversity of ARGs identified from samples collected from non-disinfected DWDSs. Furthermore, non-disinfected DWDSs contained the highest diversity of bacterial communities. However, samples from DWDSs using disinfectants contained over double the ratio of ARG reads to 16S rRNA gene reads and most of the MRG (namely mercury and arsenic resistance genes). The total reads and types of ARGs conferring genes associated with antibiotic groups namely multidrug resistance, and bacitracin, beta-lactam, and aminoglycoside and mercury resistance genes increased in waterworks treating surface water with disinfection. The findings of this study contribute toward a comprehensive understanding of ARGs and MRGs in DWDSs. The occurrence of bacteria carrying antibiotic or metal resistance genes in drinking water causes direct exposure to people, and thus, more systematic investigation is needed to decipher the potential effect of these resistomes on human health.

Highlights

Antibiotic-resistant bacteria (ARB) are a critically emerging burden for public health (Ferri et al, 2017; Ghosh et al, 2021)
A total of 430 antibiotic resistance genes (ARGs) from all water samples were identified with an average of 294, 296, 225, 272, and 232 ARGs for two samples collected in consecutive weeks at drinking water distribution systems (DWDSs) A to E, respectively
Our results indicated that disinfection during the drinking water treatment process creates selective ecological pressure for the proliferation of antibiotics and metal stress-resistant bacterial communities in DWDSs

Summary

Introduction

Antibiotic-resistant bacteria (ARB) are a critically emerging burden for public health (Ferri et al, 2017; Ghosh et al, 2021). Antibiotic-Resistant Bacteria and antibiotic resistance genes (ARGs) have long been reported in drinking water distribution systems (DWDSs) (Xi et al, 2009; Sanganyado and Gwenzi, 2019; Chen et al, 2020; Ramos et al, 2020). Biofilms function as a hotspot for horizontal gene transfer (HGT) events and dissemination of ARGs from ARB to antibiotic susceptible microbes or even to opportunistic pathogens (Xi et al, 2009; Pal et al, 2015; Chen et al, 2020). HGT is the primary mechanism for spreading ARGs among bacterial communities through the process of transformation, transduction, or conjugation and is mediated by MGE (van Hoek et al, 2011; Bengtsson-Palme et al, 2014; Sultan et al, 2018)

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Results

Conclusion