FAQ

Why do you have two different methods for the determination of E. coli and other coliforms in the form of the Coliscan® Easygel® and the Coliscan® MF ? How do they differ and how can I know which is the better one to use?

Can I do "Fecal Coliforms" with Coliscan?

Why are E. coli colonies blue/purple and Other Coliform types red/pink?

Why are some E. coli colonies more purple and others more dark navy blue?

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?

Do I need an incubator and how long should I incubate the dishes?

Is the colony size of any importance in doing my counts?

What is the maximum (and minimum) number of colonies that can be counted accurately on one dish?

How do I know how large a sample to use?

How do I do a dilution?

How can I know if information presented from studies comparing different methods is valid and that the conclusions presented with those studies are accurate and valid?

There was a notice on the box of Coliscan that said it must be frozen for storage, but when I opened the box, the medium was thawed and liquid. Do I have a problem?

The pretreated plates which I received with my bottles of Easygel® look strange. Some have water droplets covering the surface of the film on the inside bottom of the plate which gives the layer a hazy appearance. Some may also have water droplets collected in the lid of the plates in some sleeves. Is this contamination or are these plates OK to use? (Conversely, you could receive plates which are so dry that the layer on the inside bottom has the appearance of frosted glass.)

 

 

The following questions and answers may be very useful to persons who are not experienced in general microbiological methodology or the principles involved in using Coliscan media.

FAQ ABOUT THE USE AND INTERPRETATION OF COLISCAN® EASYGEL® AND COLISCAN® MEMBRANE FILTER METHODS

The Coliscan® media are nutrient formulations to grow, differentiate, identify and quantify Escherichia coli (the primary fecal coliform bacterial type) and other coliform bacteria (mainly non-fecal) as separate entities from other members of the family Enterobacteriaceae, while generally inhibiting or preventing the growth of gram positive bacteria and some other gram negative bacteria.

The following questions and answers may be very useful to persons who are not experienced in general microbiological methodology or the principles involved in using Coliscan® media.


1. Why do you have two different methods for the determination of E. coli and other coliforms in the form of the Easygel® Coliscan® and the Coliscan® MF ? How do they differ and how can I know which is the better one to use?

2. Can I do "Fecal Coliforms" with Coliscan?

3. Why are E. coli colonies blue/purple and Other Coliform types red/pink?

4. Why are some E. coli colonies more purple and others more dark navy blue?

5. 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?

6. Do I need an incubator and how long should I incubate the plates?

7. Is the colony size of any importance in doing my counts?

8. What is the maximum (and minimum) number of colonies that can be counted accurately on one plate?

9. How do I know how large a sample to use?

10. How do I do a dilution?

11. How can I know if information presented from studies comparing different methods is valid and that the conclusions presented with those studies are accurate and valid?

12. There was a notice on the box of Coliscan that said it must be frozen for storage, but when I opened the box, the medium was thawed and liquid. Do I have a problem?

13. The pretreated plates which I received with my bottles of Easygel® look strange. Some have water droplets covering the surface of the film on the inside bottom of the plate which gives the layer a hazy appearance. Some may also have water droplets collected in the lid of the plates in some sleeves. Is this contamination or are these plates OK to use? (Conversely, you could receive plates which are so dry that the layer on the inside bottom has the appearance of frosted glass.)

 


 

CHROMOGENIC MEDIA AVAILABLE FROM MICROLOGY LABORATORIES

  1. THE COLISCAN® MEDIA GROUP
    All these media are formulated for the growth, identification, quantification, and differentiation of E. coli and other coliforms. Chromogenic enzyme substrates for glucuronidase and galactosidase are incorporated in these patented media so that E. coli colonies (CFU) are one color and other coliforms are another color, while non-coliforms that may appear are either uncolored or differently colored than the target organisms (E. coli and other coliforms).

    COLISCAN® EASYGEL® (cat. # 25001)
    COLISCAN® MF (cat. # 250MF)

    These are the original formulations which have been in use since their invention and marketing in the early 1990s. They were sold as ColiChrome 2, and have been copied and imitated around the world, but due to U.S. patents, the copies cannot be legally sold in the U.S. without a license from Micrology Laboratories. In this preferred formulation, E. coli grows as blue/purple colonies (CFU) and other coliforms grow as pink/red colonies. These media are widely used in the food and water testing industries where their ease of use, rapid response time, and accuracy have made them favorites.

    COLISCAN® PLUS EASYGEL® (cat. # 25301)
    COLISCAN® MF PLUS (cat. # 251MF)


    These new Coliscan® media do everything that the original Coliscan® media do, plus they allow those who may be unsure of the difference in color of the colonies growing in the medium to very easily verify that the colony is or is not glucuronidase positive. (That is, does it have blue color verifying it as E. coli or is it just a deep magenta and therefore a general coliform?) All that is needed is a long wave UV light source (available from Micrology Labs or other sources) and a dark room for viewing.

    Your Coliscan® dishes and colonies will look identical to the original Coliscan® dishes with Blue/purple E. coli and pink/magenta other coliforms visible in ambient day or room light, but when you turn off the lights and shine the long wave UV on the bottom of the dish, any E. coli will be surrounded by a bright bluish fluorescent zone.

    This application of two enzyme substrates testing for the same enzyme means that you have double verification for the presence of E. coli. It also means that the presence of E. coli may be detected and quantified as early as 12 hours incubation time. (It must be remembered that the fluorescent zone will diffuse in the medium, so in order to quantify the CFUs of E. coli, they must be observed prior to excessive diffusion.)

    *Patents Pending

    COLISCAN® ES EASYGEL® (cat. # 25201)

    ES means "extra strength" and this new formulation was created with extra components to give it the ability to accept a 10 mL test sample instead of the 1-5 mL size allowed by standard Coliscan® Easygel®. This increases the sensitivity of the medium by up to 10X and allows a much larger sample to be tested in a single dish.

  2. THE ECA CHECK® MEDIA GROUP
    These media have been developed and formulated to enhance maximum versatility with clarity and ease of use and interpretation. For normal test samples of many types, they will grow, differentiate, identify and quantify E. coli, other coliforms, Salmonella spp., and Aeromonas spp. while inhibiting gram positive organisms and some other gram negative types.

    ECA CHECK® EASYGEL® (cat. # 26001)

    ECA CHECK® MF (cat. # 260EC)
    ECA CHECK® PLUS EASYGEL® (cat. # 26301)
    ECA CHECK® MF PLUS (cat. # 261EC)


    E. coli colonies will appear as a dark blue color and may have a slight colored halo. With the ECA Check® Plus media, they will fluoresce a bright blue under long wave UV when viewed in the dark.

    Other Coliforms will appear as lighter blue-grey colored colonies generally, but may show variation toward purplish/pink depending upon the relative amounts of the various enzymes they produce.

    Some Salmonella spp. grow as light green colonies which darken with age. (They are indole negative)

    Aeromonas spp. grow as pink (sometimes very light pink) colonies. (They are oxidase positive)

 

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