Simple test to save lives
The discovery of a bacterium in sewage treatment works in Sussex by researcher Dr James Ebdon could be the first step to a cheap and simple test for water pollution that could save countless lives around the world.
We take our unpolluted tap water for granted, but in developing countries tens of thousands of people die each year from water-borne infections that cause diseases like cholera, typhoid, dysentery, hepatitis A and tapeworms.
Many such cases occur because faeces from an infected person get into the water supply. Ideally we would test the water for all of the thousand or so organisms that might cause disease, but this is too expensive for developing countries.
A simpler approach is to look for a group of microbes, known as indicator organisms, whose presence tells us that faecal contamination has occurred and that the pathogens that cause infection in humans might be present. Current tests using indicator organisms however, cannot distinguish between human and non-human faeces – which are much less likely to carry human pathogens – so they are not accurate.
Dr Ebdon, a researcher in the School of Environment and Technology, has developed a test that can accurately identify the presence of human faeces. It costs only a few pounds, can be used in the field and gives results in a day. It could be an invaluable tool for public health programmes in developing countries.
Dr Ebdon found a strain of the bacterial species, Bacteroides ovatus, among the human waste that his team tested in sewage works. This bacterium (GB124) is about one-thousandth of a millimetre wide, lives in the human gut and leaves the body in faeces. It is harmless to humans and could now prove vitally important.
Because GB124 is found only in human sewage, its presence in a river indicates that human excrement has polluted the water. However, the bacterium dies after a day or so out of the body; more quickly than many of the disease-causing infectious organisms that also find their way into the water. So it would be unwise to drink water that had tested negative for live GB124 because it could still contain, say, dysentery or cholera bacteria.
Dr Ebdon, working alongside colleagues from the University of Barcelona, has found a way around this problem. Just as humans get viral infections like flu, so do bacteria, including GB124. Viruses called phages enter the bacterium's cells and hijack its protein-making apparatus to make copies of their body parts, which then assemble into new viruses. These then burst out of the cell, killing it as they do so, ready to attack more bacterial cells and repeat the cycle.
Dr Ebdon's test involves taking a sample of the water, passing it through a fine filter that holds back the bacteria but allows through the phages, which are about 150 times smaller – a few millionths of a millimetre in size. This filtered water is then added to a pre-prepared sample of Bacteroides ovatus GB124 grown from laboratory stocks. If there are phages in the water sample, these will kill the Bacteroides ovatus. If this occurs, the water must have been contaminated by human faeces and might therefore cause human disease.
James Ebdon on water pollution
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