Why are E. coli colonies blue/purple and Other Coliform types red/pink?
A 3. Coliscan® Easygel® and Coliscan® MF both contain 2 chromogenic compounds (X-gluc and Red Gal) known as enzyme substrates. All Coliforms (including E. coli) produce the enzyme for Red Gal, so when they grow on/in the Coliscan® media, the enzyme acts on the Red Gal and a pink/red color is produced that dyes the colonies pink/red. E. coli is unique from other coliforms as it produces the enzyme for X-gluc in addition to the Red Gal enzyme. The color of the dye that is produced when the X-gluc enzyme acts on the substrate is a teal green. However, since E. coli produces both enzymes, the color of the colonies is a combination of the teal green and the pink/red which makes dark blue/purple. There is, however, always the chance that an unusual strain of bacteria may be present and result in false negative or false positive readings. For example, the E. coli 0157:H7 does not produce the enzyme glucuronidase and so will appear as pink colonies indistinguishable from other general coliform
Related Questions
- How can I tell if a colony is really only pink and therefore a coliform, if there is a tinge of purple or blue in it (an indication of the presence of both pink and teal green) and therefore E. coli , or if it is teal green alone without any pink and therefore not a true coliform?
- Why are some E. coli colonies more purple and others more dark navy blue?
- Why are E. coli colonies blue/purple and Other Coliform types red/pink?
