Copper kills diarrhoeagenic bacteria Sudha VBP et al. Table 2. Physicochemical quality of tap-water before and after incubation in copper pot and in glass bottles Permissible limit Before After incubation Parameter (BIS/WHO*) incubation Test Control Alkalinity (mg/L) 600 25 25 25 Hardness (mg/L) 600 280 280 280 Turbidity (NTU) 10 0.47 0.47 0.47 TDS (mg/L) 2,000 700±49.5 655±35.4 690±14 Chlorides (mg/L) 1,000 35.45 35.45 35.45 Sulphates (mg/L) 400 86.5 86.5 86.5 pH 8.5-9.0 7.83±0.4 7.93±0.3 7.83±0.4 Copper content (mg/L)* 2 <DL 0.1 0.177±0.016 <DL *Detectable limit=0.02 mg/L; BIS=Bureau of Indian Standards; DL=Detecting limit; NTU=Nephelometric turbidity unit; TDS=Total dissolved solids; WHO=World Health Organization they have transformed into the viable but non- culturable (VBNC) state. VBNC is a state in bacte- ria where the cells do not grow onto routinely- employed media but are still viable (21). VBNC bacteria have been studied using several methods, including alteration in temperature (22), use of en- richment medium (23), changes in the growth medium, using chick embryo yolk sack, passage through rabbit illeal loop (13), or co-culturing with eukaryotic cell cultures (21). VBNC bacteria have been observed using viable stains (22) and microscopy (21,24,25). Studies have shown that copper surfaces completely kill bacteria. E. coli inoculated on to copper coupons were completely killed. The studies concluded that the copper ions brought about complete killing of bacteria by membrane damage (26). However, the mechanism of action of copper on bacteria is not completely understood. Although studies have shown the merits of copper surfaces for their use in improving public hygiene in healthcare facilities, the potential use of copper for the purification of drinking-water, especially in developing countries, has not been widely stud- ied. Therefore, results of our study indicate that copper holds potential to provide microbially-safe drinking-water to the rural masses in develop- ing countries. The use of copper pots in Indian households is common and is, therefore, likely to be socially accepted by the people. Its functioning is not dependent on fuel, electricity, replaceable filters, intensity of sunlight, etc. to operate or maintain it; it is simply a passive storage of water. This takes into account the conditions prevailing in rural villages and the urban slums of developing countries. The health benefit that can be achieved by using copper pot as a PoU water-purification de- vice will far outweigh the cost of the pot, if divided 20 over the members in a rural family, especially as it will be a one-time investment with no recurring costs. However, it is important to challenge its use under real-life conditions in the dynamics of the target households in developing countries to fully understand the limitations. ACKNOWLEDGEMENTS The study was supported by the ETC CAPTURED Programme, The Netherlands (Grant No. DGIS/D). The authors thank Mr. Darshan Shankar, Advisor, IAIM, for his constant encouragement. REFERENCES 1. World Health Organization. Progress on sanitation and drinking-water: 2010 update. Geneva: World Health Organization, 2010. 55 p. (WHO/UNICEF 2010). 2. Kosek M, Bern C, Guerrant RL. The global burden of diarrhoeal disease, as estimated from studies pub- lished between 1992 and 2000. Bull World Health Or- gan 2003;81:197-204. 3. Fontaine O, Kosek M, Bhatnagar S, Boschi-Pinto C, Chan, KY, Duggan C et al. Setting research priorities to reduce global mortality from childhood diarrhoea by 2015. PLOS Med 2009;6:e41. (doI:10.1371/Journal. Pmed.10000412). 4. Qadri F, Svennerholm AM, Faruque ASG, Sack RB. Enterotoxigenic Escherichia coli in developing coun- tries: epidemiology, microbiology, clinical features, treatment, and prevention. Clin Microbiol Rev 2005; 18:465-83. 5. Kanugo S, Sah BK, Lopez Al, Sung JS, Paisly AM, Sur D et al. Cholera in India: an analysis of reports, 1997- 2006. Bull World Health Organ 2010;88:185-91. 6. Sur D, Ramamurthy T, Deen J, Bhattacharya SK. Shig- JHPN