Microbiological safety of a small water distribution system: evaluating potentially pathogenic bacteria using advanced sequencing techniques

Abstract

This study evaluated the microbiological safety of the water distribution system of a city in the state of Minas Gerais (Brazil), population 120,000 inhabitants. During the study, the city suffered a severe drought that had a significant impact on water availability and quality in the river that supplies water to the city. Samples (2 liters) were collected from the distribution system over a period of six months, which included wet and dry months, from three points: the point with the lowest altitude in the distribution network, the farthest point from the water treatment works, and an intermediate point. Free chlorine was measured in situ using a Hach kit. DNA was extracted using a FastDNA Spin Kit Soil (Qbiogene). Advanced sequencing techniques (Ion Torrent) were used to identify and quantify the relative abundance of potentially pathogenic bacteria present in the samples. Coliforms and Escherichia coli, indicators currently used worldwide to assess microbiological safety of drinking water, were measured on all samples using an enzyme substrate method (ONPG-MUG Colilert®). Next generation sequencing results retrieved 16SrRNA sequences of E. coli and some potentially pathogenic bacteria, even in the presence of free chlorine. Operational taxonomic units related to pathogenic bacteria were present in all samples from the drinking water distribution system (DWS) and, in general, at high relative abundance (up to 5%). A total of 19 species related to bacterial pathogens were detected. Inadequate operational practices that could affect the microbiological safety of the DWS were identified and discussed. The current paper is the first to evaluate the community of potentially pathogenic bacteria in a real DWS.

A comparative assessment of conventional and molecular methods, including MinION nanopore sequencing, for surveying water quality

“…These discrepancies suggest that coliform bacteria were inactivated by the disinfection, but inactivated cells and/or their DNA were still present in the water. For example, DNA based methods such as qPCR and NGS (both Illumina and MinION) will not differentiate between viable and dead bacterial cells, or extracellular DNA, and therefore may have poor comparability with culture based techniques 18,31 , especially in disinfected waters. In such instances, the combined information of DNA based and culture based methods adds meaningful value to the water quality survey, because it suggests that some water samples were fit for consumption due to treatment (i.e.…”

“…However, they did not assess their method validity using samples of known composition. When applied to drinking water quality monitoring, qPCR and NGS data were not always found to be well-correlated with culture based methods 18,31 . Reliable identification of putative pathogens at species level remains a challenge, especially for water samples containing low amounts of DNA.…”

Contamination event diagnosis in drinking water networks: A review

“…In the literature, a significant volume of research has explored the short and long-term impacts of various contaminants, including trace elements (Aghlmand et al, 2021;Çiner et al, 2021;Kicinska & Wysowska, 2021;of Emergency & Response, 1989) and pathogens (Gerba, 2015;He & Huang, 2020;Organization, 2016). Specifically for pathogens, previous studies were used for estimating the risk of infection from cross-connection and backflow events (Viñas et al, 2022), pathogens contamination (Jamal et al, 2020), cryptosporidium, Giardia, and escherichia coli (E. coli) from faecal contamination in a drinking water source (Tolouei et al, 2019;Tinelli et al, 2018), faecal contamination (pathogens) events after repairs of drinking water mains (Batista et al, 2018), intentional pathogenic contamination in a WDS from consuming contaminated unboiled drinking water, and inhaling contaminated aerosol droplets when taking a shower (Schijven et al, 2016), potential treatment failures and unexpected variations in water quality and operating parameters of a water treatment plant (Hamouda et al, 2016), legionellae contamination in drinking WDNs (Hamilton & Haas, 2016;Buse et al, 2012), Campylobacter jejuni contamination (Van Abel et al, 2014) and intrusion of E. Coli bacteria during a sudden power shutdown associated with low or negative pressures (Farahat et al, 2019). In (Janne et al, 2017), models were used to track the effects of water sources on the consumers and a statistical methodology was employed to assess the public health risks of water consumption as well as the economic impacts of increased illnesses.…”

Combining physicochemical properties and microbiome data to evaluate the water quality of South African drinking water production plants

“…The application of Next Generation Sequencing (NGS) for microbial detection has a number of limitations. NGS-based methods cannot differentiate between viable and dead bacterial cells thus in disinfected water, they may have poor comparability to culture-based methods [63,64]. To overcome such limitations, it is crucial that NGS methods are combined with culture based methods which can provide an extra dimension of the cell viability.…”