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Args In Water Distribution System In Glasgow: Does The Problem Really Exist?

World Water Congress 2015 Edinburgh Scotland
13. Non-conventional sources of water
Author(s): Charles Knapp
Tara Beattie

University of Strathclyde, Glasgow1

Keyword(s): Sub-theme 13: Non-conventional sources of water,



Antibiotic Resistant Bacteria (ARB) and their genes (ARGs) are considered as well known contaminants in waste water and emerging contaminants in drinking water treatment plants [17] and water distribution system [8]. Due to the presence of pathogenic bacteria and their genes, availability of safe drinking water has become one of the key concerns of the world.

Drinking water pollution is not only prevalent in developing low income countries but also occurs in developed nations. Multiple drug resistance bacteria are found in water sample having plasmid mediate resistance [21]. In India and Pakistan, New Delhi metallo-beta-lactamase 1 (NDM-1) genes are reported in bacteria in chlorinated treated drinking water [22]. The same genes are also found in UK including England, Scotland, Ireland [12], and in USA in Michigan and Ohio [25]. Both prokaryotes and eukaryotes [3, 16, 23] are found in water. Some studies reported the presence of ARGs in treated drinking water as well [20, 25].

During treatment process, it is not possible to fully eradicate the ARGs [19]. Some resistance bacteria are found dominant in potable drinking water as compare to source water. It is also because of the fact that these bacteria live in pipelines and shed in water [3]. Plumbing system in buildings contains more bacteria as compare to source water and even in the presence of suitable amount of residual disinfectants, drinking water contains diverse type of bacteria [24]. Presence of biofilm has a role in the development of ARGs [1] as exchange of genetic material occurs through horizontal gene transfer in these biofilms [19]. Older biofilms are less susceptible to disinfection due to the physiological changes in population [13].

Main objective of this study is to find the antibiotic resistance bacteria in municipal water supply system in Glasgow at the consumer end. Our hypothesis is that resistant bacteria are present even after the application of disinfectant in treatment plant and presence of residual chlorine in distribution system. We have tried to find out the presence of transferable integrons (Int-1) and disinfectant resistant genes (qac) in the bacteria isolated from water distribution system of Glasgow. The confirmation of presence of these bacteria and their genes is an indication that water is not totally safe and there are chances of epidemics.

Materials and Methods:

Tap water samples were collected from kitchens in Glasgow and process by filtration [2]. 148 bacterial isolates were tested for Tetracycline, Sulfamethoxazole, Amoxicillin and Ciprofloxacin by Agar Dilution Method. Each antibiotic was tested with Replica Plating method and MIC values were determined [14]. Disinfectant susceptibility test was performed by Kirby-Bauer disc diffusion method [6] and suspension test. Free chlorine solutions with 5 concentrations were prepared. Bacterial was added at a concentration of 1 x 105 cfu/mL. At 0, 15 and 60 minute contact time, samples were plated on agar plate and cfu/mL was calculated. Free chlorine was determined by DPD method [18]. Monochloramine suspension test was performed similarly using PBS of pH 8.0 [5,9,10] and concentration was determined by Indophenol method [15]. DNA of bacterial isolates was extracted by freeze thawed cycles. PCR reaction was performed by primers for 16S rRNA [4], integrase gene [7] and qac genes [11]. PCR products length was verified on 2% agarose gel.

Results and Discussion:

Among 148 isolates, 128 bacteria (86.5%) show single or multiple resistant while 20 bacteria (13.5%) have no resistant against any of the antibiotic tested. 96 bacteria (64.9%) have Amoxicillin (A) resistance and they grow at > 8 µg/mL of antibiotic. Amoxicillin resistance is the most common resistance among the bacteria isolated from tap water of Glasgow. Seven (4.7%) bacteria have quadruplet resistant (TSCA) against all four antibiotics indicating that they are multiple antibiotic resistance bacteria (MDR). 11 (7.4%) have triple resistant and 56 (37.8%) show resistant against any two antibiotics simultaneously. Sulfamethoxazole and amoxicillin resistant combination is the most common multidrug resistance among bacteria in tap water as 45 (30.4%) isolates show this resistant combination. The result confirms our hypothesis that ARBs are present in distribution system. Presence of int-1 genes shows that the higher number of resistant organisms is due to the transferability of genes among bacteria.

Chlorine is the most preferred disinfectant in water treatment plants but it has a role in the enrichment of ARBs. Due to this situation, currently available disinfectants are unable to completely eradicate the pathogens or bacteria from water as found in our study that not only bacteria are present in tap water but they have transferable antibiotic resistant genes. It may be because of the reason that during disinfection process, ARBs are killed but their genes retain their activity and transfer to other bacteria.


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