Disinfectant residuals in drinking water systems select for mycobacterial populations with intrinsic antimicrobial resistance

Abstract

22Antimicrobial resistance (AMR) in drinking water has received less attention than 23 counterparts in the urban water cycle. While culture-based techniques or gene-centric 24 PCR have been used to probe the impact of treatment approaches (e.g., disinfection) on 25 AMR in drinking water, to our knowledge there is no systematic comparison of AMR 26 traits between disinfected and disinfectant residual-free drinking water systems. We use 27 metagenomics to assess the associations between disinfectant residuals and AMR 28 prevalence and its host association in full-scale drinking water distribution systems 29 (DWDSs). The differences in AMR profiles between DWDSs are associated with the 30 presence or absence of disinfectant. Further, AMR genes and mechanisms enriched in 31 disinfected systems are associated with drug classes primarily linked to nontuberculous 32 mycobacteria (NTM). Finally, evaluation of metagenome assembled genomes (MAGs) 33 of NTM indicates that they possess AMR genes conferring intrinsic resistance to key 34 antibiotics, whereas such NTM genomes were not detected in disinfectant residual free 35DWDSs. Thus, disinfection may not only influence the AMR profiles of the drinking 36 water microbiome but also select for NTM with intrinsic AMR. 37 38 39 Regulation compliant drinking water can contain low concentrations of chemicals and 41 microorganisms originating from source water, treatment process, distribution systems, 42 and premises plumbing 1,2 . While our understanding of chemical contaminants (e.g., 43 disinfection by-products (DBP) 3 ) and microbial populations 4-6 in treated drinking water 44 is increasing, the drinking water field has only recently started investigating emerging 45 biological contaminants 7 like antibiotic resistance bacteria (ARB) and antibiotic 46 resistance genes (ARG). Misuse of antibiotics and anthropogenic release of bioactive 47 compounds into the urban water cycle exacerbate the prevalence and persistence of 48 antimicrobial resistance (AMR) and can make engineered systems for water treatment 49 (i.e., wastewater and drinking water) critical points of AMR dissemination 8,9 . Drinking 50 water can constitute a potential exposure route to microorganisms with intrinsic and 51 acquired antibiotic resistance genes (i.e., resistome 10 ), and it is particularly concerning 52 if AMR traits are associated with waterborne pathogens 11 . 53 54Drinking water disinfection is one of the most important public health advances towards 55 elimination of waterborne diseases and remains the most widely used treatment strategy 56 today for pathogen control 12 . Typically, drinking water systems (DWS) maintain a 57 disinfectant residual, usually chlorine, in the drinking water distribution system 58 (DWDS) to minimize microbial growth. However, its unintended impacts (e.g., DBP 59 formation) have prompted the evaluation of alternative strategies to mitigate associated 60 risks. These range from the use of alternate disinfectants such as chloramines, to 61 advanced oxidation processes th...

Uncharted waters: the unintended impacts of residual chlorine on water quality and biofilms

“…However, ecological indices are reductive and can only evidence major differences between community structures, the findings in the current study (which benefitted from using the same water source between experiments) are indicative that changes in the biofilm microbiome between chlorine regimes were more subtle. Disinfection is known to alter planktonic bacterial community compositions [10][11][12]19 and has previously been demonstrated to also shape the succession of biofilm bacterial communities during growth (there was less of an impact of chlorine on fungi) within the DWDS test facility used in this study, even when the inoculum was pre-conditioned by being chlorinated water 16 . In the current study, pre-flush and post-flush data were analysed ( Fig.…”

“…calculated the contact times required to inactivate various microorganisms (assuming 0.5 mgL −1 chlorine, pH7 and 5°C), concluding that the disinfectant contact times within DWDS are likely ineffective in their inactivation. These sublethal doses of disinfectant can then exert a selective pressure and various research studies have shown that the presence, type and concentration of disinfection impacts the planktonic bacterial composition of drinking water, enriching or decreasing certain functional genes or bacterial taxa [10][11][12] . Similarly, comparison of regulatory water sample compliance illustrated that the USA, which uses chlorine residual disinfection, had 10 times more total coliform failures than the Netherlands, which does not use a disinfection residual 9 , this is after adjusting for population, although there are other differences beside disinfection between the systems (e.g.…”

Disinfection exhibits systematic impacts on the drinking water microbiome

“…The membranes were stored at 4°C for 24 h or less before being transported to the laboratory and stored at − 80°C. Further details of sample treatments and preservation are described in Sevillano-Rivera et al [35], along with detailed description of chemical analyses. Briefly, Orion 5 Star Meter (Thermo Fisher Scientific, Waltham, MA) was used to measure temperature, pH, and conductivity, and dissolved oxygen, while total chlorine and phosphate were determined on-site using DR 2800 VIS Spectrophotometer (Hach Lange, the UK) and EPA-approved HACH kits.…”

“…Negative controls consisting of reagent blanks (no input material) and filter blanks (filter membranes from unused Sterivex filters) were processed identically as the samples for DNA extraction. Genomic DNA extracted from mock community, consisting of 10 organisms, detailed previously [35], was spiked into negative controls extracted (n = 8) from the reagent and filter blanks. These negative controls were also included in following library preparation and high-throughput sequencing (see below).…”

“…These include esthetic and corrosion related problems [25,27,28] but more importantly the formation of harmful disinfection byproducts (DBPs) [29][30][31], which are also regulated. Further, there is an increasing recognition that the disinfectant residuals may be associated with selection of some opportunistic pathogens [16,32] and antibiotic resistance genes (ARGs) in drinking water [33][34][35].…”