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?
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?
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?
- Both the Easygel® and the MF approaches work very well when used properly. The Easygel® is provided as a liquid medium which contains a gelling agent that causes the medium to solidify when it is poured into a petri dish containing a layer of calcium ions so that it resembles a standard prepoured agar plate. The gelled dish can be streaked or swabbed with test material or a small test sample (generally 1-5 mL) can be added prior to pouring. The MF consists of a liquid medium without a gelling agent which is used to saturate a sterile pad in a small petri dish in conjunction with a micropore membrane filter which has filtered an aqueous test sample, with the sample generally being of a larger volume. Both approaches use very similar formulations and ingredients with the exception of the gelling agent. (For those familiar with the membrane filter approach where the medium is agar based and a solid layer is formed in a dish as the foundation for the membrane filter, Coliscan® can also be prepared in this manner. It is not currently offered in this format other than by custom request.)
The Easygel® is designed for use when the number of target organisms/mL of sample is quite high and therefore the number of colony forming units/plate will be high enough to count with accuracy when a 1-5 mL sample is added directly to the medium. That is, the medium will only have a sensitivity of one CFU/mL or one CFU/5 mL if straight water samples are used directly. This means that with a 5 mL sample, a population of 20 viable target organisms/100 mL (one organism in 5 mL)of sample will be the lower level detected. That is quite sensitive, but it will not meet the requirements of zero E. coli /100 mL which is the federal standard for drinking water. Therefore if very high sensitivity is required, the MF method is best. However, most environmental surface waters have a significant number of E. coli /mL so a small sample will result in an accurate reflection of the #/given volume. (Most environmental water watch volunteers translate their data into #/100 mL) If a 5 mL water sample consistently results in no E. coli colonies and you need to know if there are actually a few/100 mL present, you will need to either do at least 5 replicate plates with 5 mL samples for the Easygel, or you should switch to the MF approach where you can do any size sample/plate. (Note also the availability of the new Coliscan®Easygel® ES medium which will accommodate a 10 mL test sample and therefore has a sensitivity of 1 viable target organism/10 mL of sample.)
Therefore, you can see that the MF is designed for situations where the test sample has very low numbers of target organisms and it is necessary to validate the absence or very low count of the target organisms, while the Easygel approach is excellent for determining populations of target organisms when they are commonly present in relatively large numbers in the test materials. The MF approach will work very well even when there are large populations of the target organisms, but it becomes necessary to do dilutions of the raw test sample so that not too many CFUs occur in/on one plate.
- Yes. The term "Fecal Coliform" just refers to coliforms that will grow at the elevated temperature of 44.5̊ C. Most strains of E. coli will grow at that temperature, and there are some other coliforms that may be of fecal origin also. So if you have an incubator that can be set at 44.5̊ C, you can do "fecals". However, the protocol is for a two hour first incubation at 35̊ C before putting at the higher temperature, and if the incubator is an oven, you should seal the plates in a plastic bag so that they do not dry out during incubation. Proper protocol calls for a water bath incubator.
It should be pointed out that the Coliscan media are superior to other recommended "fecal coliform" methods because the Coliscan media not only identify the presence and quantity of "fecal coliforms", but differentiate between E. coli and other types of "fecal coliforms". That is, the E. coli are always of fecal origin and they will appear as purple or dark blue colonies, while other "fecal coliforms" will appear as pink colonies and any other non-fecal organisms which are temperature tolerant that might grow on the medium will be white or colorless. The "total fecal coliform" for the Coliscan media is the sum of the blue and the pink. This differentiation between the blue E. coli and the pink other "fecal coliform" can be important as there are numerous other strains of coliforms that are not of fecal origin that are temperature tolerant, so if no temperature tolerant E. coli show up on the plate, but pink temperature tolerant colonies are present, the fecal origin should be questioned.
Coliscan® media are superior to the medium developed and approved by the USEPA for the detection of fecal coliforms. A comparative discussion of this may be found on the Micrology web site.
- 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 coliforms. But the majority (estimates range from 93-97%) of E. coli types fit the typical pattern so that makes Coliscan a very reliable test method. Also, certain strains of other members of the family Enterobacteriaceae (some Salmonella and Shigella) may produce the enzyme glucuronidase, although they do not produce galactosidase and therefore appear as teal-green colonies. These teal-green colonies do appear different than the general blue/purple E. coli, and fortunately another easy test screen for these various unusual bacterial types is available and may be used for verification after the initial readings. This is a spot test for the presence of indole, which is produced by virtually all strains of E. coli, but very few general coliforms or other members of the family Enterobacteriaceae. Placing a small drop of Kovacs Reagent on the test colony will result in the formation of a cherry red zone around the colony within 5-10 seconds if indol is produced. Thus, all E. coli (including the non-purple O157:H7) will have the red zone, and non-E. coli (such as the teal-green Salmonella or Shigella) will not have the red zone. This simple additional test eliminates almost all possible false readings and adds further precision to the already excellent Coliscan MF method.
Sometimes wastewaters or general surface waters also contain bacteria closely related to the coliforms which may grow on the Coliscan MF medium. Two that are common are Pseudomonas and Aeromonas species. Pseudomonas species are galactosidase and glucuronidase negative so colonies are not colored pink or purple, but they generally produce their own water soluble bluish, greenish or yellowish pigments which form a diffused colored zone around colonies. A heavy growth over a membrane filter may give the entire normally white filter a colored appearance. Colonies producing the soluble pigments described are very easily verified as non-coliforms with the oxidase test. A small drop of colorless reagent (1% aqueous tetramethyl-p-phenylene diamine)on the colony gives a dark purple zone around the Pseudomonas colony within 15 seconds. Coliforms are negative and develop no color. Aeromonas species are generally galactosidase positive and therefore grow as pink colonies like the general coliforms. However, if Aeromonas is suspected, they too can be easily differentiated from coliforms with the oxidase test. With the test reagent, Aeromonas colonies will develop a deep purple zone like Pseudomonas.
It is possible to eliminate most of these organisms from growing on the Coliscan MF medium through the use of various inhibitors and temperature control. However, they do not generally cause a problem with the general analysis. E. coli will still grow as deep blue/purple colonies and debate continues on the importance of Aeromonas with many believing that it is as important an indicator as general coliforms. Likewise, the presence of Pseudomonas in water can be important from a sanitation and medical perspective.
- The reason for this is that there are thousands of different strains of E. coli found in the environment, and some produce more of the one enzyme and less of the other. So if a lot of the Red Gal enzyme and only a small amount of the X-gluc enzyme is produced by a strain, the color will be more purple (and will commonly have a pink halo surrounding it), while if less Red Gal enzyme and more X-gluc enzyme is produced the colonies will be dark blue (and will commonly have no noticeable pink halo). Therefore, any colony that looks blue or purple is E. coli because that indicates that both enzymes are produced. Teal green colonies are technically not coliforms, but are likely closely related organisms like Proteus or Salmonella or an unusual form of E. coli. The only way to determine the identity of these is to run further biochemical tests, which should be done by a qualified technician or lab.
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?
- First of all, you should be aware of the fact that E. coli colonies appear earlier on the plate that the other coliforms. This is because the E. coli produces both enzymes and therefore a double dose of dyes which give quicker, darker color, while the other coliforms only produce the one enzyme and the lighter pink color is produced by its activity. So E. coli is visible first and has a definite blue tone, while the other coliforms appear a bit later and look pale pinkish at first. (Teal green appear later also and look very pale green with a light green halo at first.)
Second, true teal green colonies will never have a pinkish halo around them, but only a light green halo. True E. coli will either have no noticeable halo or the halo will tend to have a definite pinkish color.
If you are still not sure of which colors are associated with the colonies that you are seeing, you can purchase Micrology's "Test Media for the Determination of E. coli from Coliforms". There are 2 different media available which, when used together, will tell you if the colony in question is producing the X-gluc enzyme, the Red Gal enzyme, both enzymes, or neither enzyme. You will need to acquire at least one set of confirmation media (#25101). This approach is the best to use with colonies growing in/on Easygel® Coliscan® medium.
If you are using Coliscan® Membrane Filter medium, the confirmation of E. coli is very easily done by depositing a very small drop of Kovacs Reagent on the colony to be tested. This is a test for the presence of indol, which E. coliproduces and other coliforms do not generally produce. Therefore, a cherry red spot will develop around E. coli colonies within ten seconds. ( See the Micrology home page for indol to see a photo.)
Last, the use of Coliscan® Easygel® Plus or Coliscan® MF will verify the presence of absence of glucuronidase in a colony.
- An expensive commercial incubator is not necessary to obtain excellent results. However, conditions do need to be warm enough for the microbes to grow in the medium after the sample is added and the plates have been poured and gelled. Therefore, the plates should be kept in a warm area (preferred minimum temp. 80-95̊ F) to allow growth. This could be in a box over a hot air heat register, or better yet in a foam box where you have placed a bottle of very hot water (when the lid is closed tightly, the heat will diffuse out of the water and warm the inside of the box to a good incubation temperature and hold it for 8-10 hrs, at which point, you can renew the hot water for further incubation as needed.) Some persons make their own incubators by installing a heat tape, or a light bulb inside a foam or cardboard box, which will hold the temperature steady. However if a light bulb is used, shield the plates so the direct light doesn't hit them and be sure that the bulb is not touching anything that it might ignite. You should try to achieve as stable, constant temperature as possible in the area of 85-95̊ F for most purposes to induce the fastest growth. If you are not using a thermostatically controlled incubator, you should check the plates at intervals, beginning at 24 hr, until you see some blue or pink spots developing. Then allow the plates to incubate another 24 hr and do your counts.
We highly recommend the purchase of a small, inexpensive egg incubator which works extremely well. These can often be found at farm stores for less than $40, and our favorite is made by G.Q.F. Manufacturing of Savannah, Georgia. (Phone 912-236-0651, Model # 1602N Hovabator Incubator). These come with an adjustable thermostat and thermometer and we have had one operating in our lab for more than 10 years with no problems. If you are doing ongoing testing, the price is certainly right, and having one of these units eliminates any question of variations from big temperature fluctuations during the incubation period. If you set your incubator at 35̊ C., you should be able to count results as early as 24 hr after placing the plates in the incubator. Do not count any colonies that may develop after 48 hr as the E. coli and coliforms that you are monitoring are very fast growing and will definitely be visible within that time period.
- Yes. Colony size is related to several factors.
First, you need to know that E. coli and other coliforms grow very rapidly when compared to most other bacteria, so they generally appear in the plate first. Any colonies that appear after 48 hours should be disregarded.
Second, if you are incubating at lower temperature ("room temp"), the colonies will not appear as soon. In this case, you should wait until you are seeing the first colored colonies and then give at least another 18-20 hours for further growth and development of color before counting the results.
Colonies that do not grow past a pin point size (less than 0.25 mm) within 48 hrs at 35̊ C. should not be counted without further testing, especially if they were late showing up. An exception to this rule is if there are so many colonies in the plate that it is covered with colonies very close together. Such a plate can even look like it doesn't have any colonies at all and just have a pink or bluish cast throughout the whole plate.
Colonies growing down in the solid medium will be smaller than those growing on the surface and surface colonies generally are paler in color. Also, if colonies are crowded close to each other on/in the medium, they will not grow as large.
Rarely, there may be present a large colored spot growing on the surface or under the medium on the plate. This is usually the result of a colony growing at the edge of the plate and down under the medium where there may be excessive moisture where it can spread, and it should be counted as only one colony forming unit.
- Standard protocol for most samples dictates that Coliscan®Easygel® dishes containing more than 300 colonies (CFU) should be identified as TNTC (too numerous to count). However, it is possible to achieve quite accurate results or estimates with up to 1000 colonies/plate by careful observation. Standard protocol for Coliscan®MF dishes dictates a maximum of 80 CFU/dish due to the fact that the MF dish is a much smaller diameter (60 mm vs. 100 mm for standard dishes). It should also be noted that less than 20 CFUs/dish for either medium is considered to be statistically questionable for accuracy of count. (Note that Coliscan® Easygel® and other Easygel® media types used as pour plates in food and water testing have a big advantage over methods such as 3M's Petrifilm® and Hach's Coliblue® media which are limited to a small sized surface area for colony growth.)
The best way to count colonies is to position a light source so that you can easily see the colonies while looking through the bottom of the plate, and then mark each colony with a dot from a "sharpie" fine tip felt pen as you count it. That way, you avoid double counting.
- You have to experiment or use past experience. When using Coliscan®Easygel® with surface waters such as lakes and rivers, we suggest starting with 1 mL/plate. If you know the water to be low in bacteria, you can add up to 5 mL/plate.
Water samples that have very large numbers of target organisms (E. coli) may need to be diluted before adding to the medium. For example, if there are 500 E. coli /mL of the water being tested, the use of a 1 mL sample would result in 500 E. coli colony forming units in one plate which is too high. Therefore, a 10X dilution of the water would be desirable and 1 mL of the 10X dilution would result in 50 colony forming units/plate, which is more countable and will generally result in better accuracy. That dilution will also reduce the numbers of background organisms which is good.
If you are testing samples with very low numbers of bacteria (for example, less than 1/mL) it would be advisable to use the Coliscan®MF medium.
- You need a sterile measured diluent (Micrology Laboratories has diluents available, or you can make your own). The simplest way (-but not the best if you want your study to meet official protocol standards-) is to boil some distilled or deionized water to "sterilize"it. This will kill any coliforms that may be present. Measure out 90 mL in a sterile container and cool. When cool, add 10 mL of your water sample to the 90 mL of diluent, replace the lid and shake at least 25 times. Open and use 1 mL of the diluent-sample mix in your medium. When you count the target organisms, you will need to multiply the # of colonies X 10 to calculate how many there were in 1 mL of original undiluted water sample. (If there were 50 E. coli colonies growing in the plate, there would have been 500 E. coli /mL in the original undiluted water sample.)
For more information on dilutions click here.
- We have received or seen data and comments from numerous sources which profess to evaluate and assess the accuracy and ease of use and interpretation of our Coliscan media. While we acknowledge that some directions and experience are invaluable for interpretation of the colony colors, we believe that the Coliscan methods are second to none in their usability and accuracy. In fact, well designed studies support this thesis. Unfortunately, many persons have tried to draw conclusions from inadequate data drawn from poorly designed or executed studies. A few of the commonly encountered pitfalls follow.
A. The first factor is the lack of replications. Any comparative study should be based upon a minimum of 3 replications. This means that at least 3 identical samples from the same test sample should be run both on the Colican medium and on each of the other media with which it is being compared. Replications are necessary to determine the absence of operator error in following proper and prescribed protocol. For example, for a comparison to be valid, there should be one large test sample from which all replications for all media are drawn, and they should all be done within a short time span of each other under the same conditions by the same operator. The sample cannot be split and part of it mailed to an outside lab while the rest is used on site. (That could result in totally different viable populations of the target organisms as well as significant differences due to different operators.)
B. A very common error is trying to validate a method with inadequate data. For example, the presence of a very small number of actual colonies for the target organism/plate will generally result in large magnitudes of apparent variation. When less than ten colonies are present, a difference of 1 or 2 colonies results in possible significant variation. That is, if the sample size is 1 mL and one plate had 6 colonies and another plate had 8 colonies, the #/100 mL would be 600 and 800 respectively. That seems like a large amount, but with such small numbers of colonies, it is probably not significantly different. And if the sample size is 1 mL and one plate had 1 colony and another 3 colonies there is a 300% variation which looks very bad when it is presented in a table or graph that doesn't note the actual numbers of colonies originally present. This can be very misleading and result in extreme, incorrect bias.
This is why most studies designed for use in approving a method will specify the minimum and maximum numbers of target colonies/plate as part of the general protocol. For example, the number for the membrane filter method is generally stated to be 20-60 /plate.
C. Another factor which may be involved in a study is variation in the types of organisms present in the test samples. Samples which are taken from the natural environment may have very large populations of one particular organism and be lacking in other types so that a study based upon samples from one or two sites may be lacking in the variety needed to test the method well. Conversely, studies based upon samples which are spiked with known varieties or organisms may not include some types that could result in false positive or negative errors so that an apparently excellent method (from the study) may be less than excellent when natural samples are used that contain more bacterial types.
These are only several factors to consider in evaluating a method and it is obvious that care must be taken to eliminate as many variables as possible so that test results are truly significant and don't just appear to be significant and valid due to poor design, execution and interpretation of the study in question. Statistical analysis is a useful tool, but when data are manipulated or applied incorrectly due to poor initial design, the results can be very misleading. Often, what is not addressed may be more important than what is addressed. For example, one well known method advertises "low false negatives" while failing to mention that one of their own studies which was published reported over 50% false positives for total coliforms.
D. Some persons have tried to compare the Coliscan Easygel and the Coliscan MF approach/method to other methods that claim to differentiate and quantify E. coli from Other Coliforms. Two such methods are the ColiBlue® membrane filter medium of Hach and the PetrifilmTM EC medium of 3M. Each has limitations involving such things as sample size and ease of use and interpretation. One major factor of which you should be aware is that both of these media appear to be similar to the Coliscan media as they claim that E. coli appear as blue colonies and Other Coliforms are red. However, their technology must be different from that of the Coliscan media because Micrology Labs owns the exclusive rights to the patents for the simultaneous use of 2 chromogenic enzyme specific substrates to differentiate E. coli from Other Coliforms in a single medium. So instead of using X-gluc and Red Gal (Coliscan's patented combination), they use X-gluc and a tetrazolium salt combination in their media. This means that their counts for E. coli may be accurate due to the X-gluc, but the tetrazolium salt colors all other bacterial colonies a red color, whether they are true coliforms or some other related bacteria. This is why they get no different shades of blue/purple with their E. coli and why all their "coliforms" are a uniformly dark red color, which looks very nice on the plate. They claim to include inhibitors which prevent non-coliforms from growing, but this may not be entirely possible as there are numerous bacterial types which are non-coliforms that will grow in virtually any environment suitable for coliforms. As a result, these "copycat" media may be subject to high false positive errors in the identification of total coliform counts and general coliforms. (In a 1997 publication authored by Grant of the Hach Company, he admitted to 52% false positive results for total coliforms with the m-ColiBlue 24® medium.)
Studies need to be carefully examined to determine that they lack design and data flaws, and when a method is tested, technicians should be sure they understand the technology and any potentially negative flaws. For example, microbes may be inhibited by tetrazolium salts in a medium. Work done at Micrology Labs comparing identical media and conditions, but adding tetrazolium salt to one, have resulted in generally lower recovery of organisms on the medium containing the tetrazolium salt.
- No, you do not have a problem. The medium can be thawed for 2-3 weeks at room temperature with no adverse effects. Just put the bottles of liquid Coliscan in the freezer and they will be fine. Also, if you happen to thaw too many to use, they can be re-frozen without any problem. We have kept Coliscan for a month at room temperatures without noticeable negative effects, but for long term storage life, it is best frozen as the chromogenic substrates slowly lose their brilliant color over time at high temperatures.
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.)
- No, this is not contamination, but a result of shipping and storage conditions which caused a big temperature swing within the sleeves of plates, resulting in condensate forming from the water in the pretreatment layers. When this does happen, it is usually minimal and all the moisture is retained within the individual plates involved, so there is no introduction of contaminants into the plates. The plates can be used with confidence that they are not contaminated . On rare occasions, conditions get so extreme that excessive condensate runs out of the plates and causes the inside of the plastic sleeve containing the plates to become wet. Even though this environment should still be sterile, it only takes a single spore to grow and multiply so that the entire sleeve can become contaminated (worst scenario), and we recommend that you notify Micrology Labs and request replacement if this wetting of the entire inside of the plastic sleeve occurs. . (The dry, frosted appearing plates will perform well and your results will not be adversely affected. This happens when they are stored in very dry conditions.)
CHROMOGENIC MEDIA AVAILABLE FROM MICROLOGY LABORATORIES
- 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.)
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.
- 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)