Key points from article :
E. coli bacteria given genes that are sensitive to tetrathionate - an indicator of ulcerative colitis.
In presence of tetrathionate, bacteria switch on a gene to make an enzyme which is passed in faeces.
Enzyme can then be identified in lab tests, in which it changes colour.
Different colours could allow people to check their own faeces for multiple diseases.
The study was published in the Nature Biotechnology journal.
