Chromogenic Media - A Concept Pioneered by
RCR Scientific and Micrology Laboratories
ColiChrome® Redigel® and its 1990 introduction to the world stands as the first example of a microbiological medium based upon the patented (5,210,022 and continuations) invention of using two chromogenic enzyme substrates in one medium where the products were of two different, contrasting colors that were virtually insoluble in/on the solid medium. The ColiChrome® medium was invented by Dr. Jonathan Roth, a founder of RCR Scientific, Inc., and is now known as Coliscan® Easygel® that is offered by Micrology laboratories L.L.C. which is directed by Dr. Roth. Over the last two decades, Jonathan Roth and Geoffrey Roth have collaborated in the development and patenting of numerous additional chromogenic media, some of which are currently offered by Micrology laboratories and their distributors. The principle of Roth's invention has been copied world-wide and virtually all chromogenic enzyme substrate media based upon producing two or more insoluble colors which are currently available anywhere that test for E. coli and other coliform bacteria, are copies of Roth's invention.
Prior to the invention of Coliscan®, there were media using a single chromogenic enzyme substrate such as X-gal, which resulted in a single colored colony type for coliform bacteria, and there were media which utilized a chromogen and a fluorogen in combination (for example Colilert®, but which were not suitable for optimum use in solid media because the product(s) diffused quickly in the medium and made differential quantification of colonies very difficult.
The use of Chromogenic and fluorogenic enzyme substrates increased the sensitivity and accuracy of identifying and quantifying specific microbes over the older approaches that were based upon the fermentation of a sugar that produced acids that were detected with pH indicators in the media. (Examples such as VRB, MacConkey, EMB, Endo)
Just because a medium incorporates chromogenic or fluorogenic enzyme substrates does not mean that it results in definitive, easy to read results. Many media of this type result in very difficult to discern color differences, and are not specific enough to prevent numerous false results occurring from non-target organisms. Micrology Laboratories has refrained from offering chromogenic media which are subject to those problems.
Clarification of Chromogenic Ingredients in Micrology Laboratories' Media
Whenever a formulation of Micrology laboratories' medium includes at least one chromogen, the predominant chromogen may be the only chromogen listed by name, or the designation "chromogenic mix" maybe used. Whenever only a single chromogen is listed as an ingredient in a Micrology medium, the assumption should be made that the formulation may contain a "chromogenic mix" which does not state the exact chromogens used in the medium or their amounts as this is considered proprietary information.