Oxoid Brilliance E. coli/coliform Selective Agar is a chromogenic medium for the detection and enumeration of E. coli and other coliforms from food and water samples. Chromogenic agents within the medium are used to detect the ß-glucuronidase activity of E. coli and the ß–galactosidase activity of coliforms (including E. coli), allowing them to be clearly differentiated on the culture plate (coliforms – pink, E. coli – purple).