An exploration of bacterial communities in drinking water during distribution, using flow cytometry (FCM)

Abstract

Bacteria in drinking water distribution systems have aroused considerable attention due to the potential public health risks. Drinking water presents a low-nutrient environment in which various bacterial populations proliferate. Water treatment plants are designed and operated to produce safe drinking water and to protect the drinking water from microbial contamination. To ensure the safety of the drinking water from a microbiological perspective the raw water is subjected to multiple physiochemical and biological treatment processes. A variety of bacteria regrow during the process or after distribution and concentrations of 104- 105 per ml drinking water are commonly found. The microbial water quality is often assessed by the conventional cultivation-based technique, heterotrophic plate counts, (HPC) but this method suffers some limitations. Only less than 0, 01 % of the total drinking water bacteria can be detected by HPC and this method is time consuming. Flow cytometry coupled with fluorescent staining has widely been applied to assess the microbial water quality. This study, analyzed the bacterial community in drinking water distribution systems using fluorescent staining of bacterial cells with nucleic acid stains (SYBR® Green I and Propidium iodide) together with flow cytometry.
Changes in the bacterial community were observed in the drinking water during distribution. The reference water samples at the outlet of the water production storage at Vombverket treatment plant contained higher total bacterial cell concentration and % of intact bacterial cells (TCC 569 × 103 cells mL-1, % IC 70) than the other two treatment plants i.e. Ringsjöverket (TCC 162 × 103 cells mL-1, % IC 12) and Bulltofta (TCC 259 × 103 cells mL-1, % IC 48).Drinking water distribution systems, Lund and Eslöv that receives drinking water from Ringsjöverket, treatment plant showed elevated total bacterial cell concentrations and % of intact bacterial cells compared to the outgoing water from Ringsjöverket while changes in % of HNA bacterial cells was not significant. The average total bacterial cell concentration in total 34 water samples collected at Lund and in 13 water samples collected at Eslöv are estimated to 188 × 103 cells mL-1 and 168 × 103 cells mL‒1 respectively. The average % intact bacterial cells in 34 water samples collected in Lund and in 13 water samples collected in Eslöv are estimated to 32 % and 43 % respectively. A decrease in the total bacterial cell concentrations and % of intact bacterial cells was observed in water samples collected in Malmö and Dalby/Lund compared to Vombverket. The average total bacterial cell concentration in total 51 water samples collected at Malmö is estimated to 467 × 103 cells mL‒1 and in 10 water samples collected at Dalby/Lund is estimated to 557 × 103 cells mL‒1. The average % intact bacterial cells in 51 water samples collected in Malmö and Dalby/Lund are estimated to 59 % and 58 % respectively. The percentage of HNA bacterial cells in water samples collected at the latter distribution systems decreased in comparison to Vombverket, however these changes were not substantial. The impact of the decreased temperature on the % of HNA bacterial cells was observed in samples collected in drinking water distribution systems Lund and Malmö. The % of HNA bacterial cells decreased in the majority of the samples collected at these distribution systems. However, no correlation was established between reduced temperature and total bacterial cell concentration and % of intact bacterial cells.

Popular Abstract

Water is the most common and important chemical compound that is essential to sustain life on Planet Earth. Throughout our planets’ existence water has affected all the aspects around the world. 97, 5 % of the planets water resources is salt water. The remaining of the global water amount is fresh water and constitutes 2, 5 %. About two-thirds of the fresh water resources are mainly localized on the North and South poles and on the mountains in the form of glaciers which makes it almost inaccessible for human use. Thus, only less than 1 % of the planet’s total water amount is available as potential drinking water and can be used by humans. Worldwide more than one billion people don’t have access to safe drinking water. Currently, more than 40 countries around the globe are affected by an absolute water scarcity. In Europe and the US a fifth of the population drink contaminated water.
To produce safe drinking water and to protect the drinking water from microbial contaminations the water treatment plants makes use of numerous methods including physical, chemical and biological barriers. Ringsjöverket which provides drinking water to Helsingborg, Eslöv and Lund, among other cities, uses the source water from Lake Bolmen while Vombverket that delivers drinking water to Malmö and Svedala, among other cities, treats the source water from Lake Vomb. Ringsjöverket and Vombverket make use of different treatment processes including the type of chlorination which is a final treatment process step that secure the absence of viable bacterial cells in the distributed drinking water.
In order to make sure that the drinking water is safe to consume, the microbiological water quality is examined with a method involving cultivation of microorganisms called heterotrophic plate counts (HPC). Drinking water contains high concentrations of bacteria, most of these being harmless to human health. Not all drinking water bacteria are cultivable, hence can’t be detected by HPC. In fact, only a small fraction (less than 0, 01 %) of the total bacterial cells in water can be detected by HPC. “Indicator” organisms e.g. Escherichia coli and coliform are also often targeted to ensure the bacteriological safety of drinking water. These cultivation based method takes days to acquire the results.
In this thesis, a method called flow cytometry in combination with DNA staining was used. Flow cytometry (FCM) is a cultivation independent, fast and sensitive method that has already been successfully used for the analysis of bacteria in drinking water.
In short, the DNA of bacteria in a water sample is stained with a fluorescent dye that will emit light and can be counted. Water was sampled at distribution systems Lund, Malmö and Eslöv and subsequently compared to outgoing water at Ringsjöverket and Vombverket. All samples were examined using FCM. This research was done to explore the bacterial community in drinking water distribution systems and to investigate the potential impact of the distribution systems on the drinking water quality. The FCM analysis showed that the bacterial community is affected to some extent by drinking water distribution systems. The bacterial counts and % of intact bacterial cells were elevated in the distribution system, Lund while a decrease in the latter parameters was observed in distribution network, Malmö.

• author: Rahmani, Malaley
• supervisor: Kristjan Pullerits; Catherine Paul
• organization: Applied Microbiology; Biotechnology
• course: KMBM01 20162
• year: 2017
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: drinking water, bacteria, flow cytometry, applied microbiology, teknisk mikrobiologi
• language: English
• id: 8933170
• date added to LUP: 2018-03-12 11:08:01
• date last changed: 2018-03-12 11:08:01