Original source: New Scientist
Checking the hue of your faeces could soon reveal why you are feeling off-colour. Gut bacteria in mice have been genetically modified to make coloured pigments when they detect the presence of disease. If the mice have a gut disorder, the microbes turn blue.
A similar approach could be used to diagnose inflammatory bowel diseases or colon cancer in people.
At the moment, many gut disorders are diagnosed by putting a camera on a thin flexible tube up the rectum. “People often don’t like that,” says Pamela Silver of Harvard Medical School in Boston. And preparing for the procedure requires fasting and taking strong laxatives.
An alternative could be to measure chemicals in the gut that are linked to disease states. The idea of using colour-changing bacteria was mooted by a team at the University of Cambridge in 2009. But it has been difficult to develop bacteria that survive in the gut for long enough to be useful.
Now Silver and her colleagues have used a harmless strain of E. coli bacteria, which are often found in the guts of humans and mice. The team gave these bacteria genes that are sensitive to a chemical called tetrathionate, which is seen in higher levels in the guts of people with ulcerative colitis.
When the bacteria come across tetrathionate, they switch on a gene to make an enzyme, which is passed in faeces along with the bacteria. The enzyme can then be identified in lab tests, in which it changes colour.
Silver’s team gave their modified bacteria to healthy mice and to mice that had gut inflammation, similar to that seen in ulcerative colitis. The bacteria reproduced in the guts of all the mice, forming a colony that survived for at least six months.
Some bacteria get passed out of the body in faeces, and lab tests revealed the colour-change enzyme only in samples from animals with gut inflammation. In these samples, the bacteria changed colour from white to blue.
The modified bacteria have to be isolated from faeces and grown in the lab for a day before the blue colonies can be observed. But Silver says that genes for different coloured pigments could be inserted into bacteria, including fluorescent ones that people will be able to see in their own faeces.
“As a proof of concept, it’s a pretty major advance,” says Paul Freemont of Imperial College’s Synthetic Biology Hub in London.
David Riglar at Harvard Medical School, who worked on the project, hopes that the modified bacteria could help diagnose some of the many diseases that have been linked to gut bacteria, such as Parkinson’s disease and autism.
Journal reference: Nature Biotechnology, DOI: 10.1038/nbt.387