A number of products are available commercially for the detection of various coliforms via the visual appearance of colonies on chromogenic media (such as colony fluorescence under visible and/or ultraviolet light). These products are adequate for many purposes. However, often non-target micro-organisms, specifically Aeromonas spp, can also be growing, and these may be incorrectly counted as coliforms giving a false positive result.
On some commercial products these false positives arise because the formulation uses the same combination of enzyme substrates that were developed and used by a Roth Bioscience predecessor, RCR Scientific, Inc, in the late 1980s. For example, where the galactoside is used as the marker for coliforms, Aeromonas spp can be present and provide a nearly identical chromogenic pink/red response. This results in the test sample being reported to have a higher number of coliforms than is actually the case.
The R-CARD® ECC-A from Roth Bioscience, however, delivers more accurate coliform detection. Aeromonas species, if present, are initially virtually undetectable, showing as light yellow colonies that are very hard to detect against the R-CARD® background.
The best way to determine if Aeromonads are present is to make a side-by-side comparison of the test sample, one on R-CARD® ECC-A and one on R-CARD® ECC (E. coli and coliforms), and count the coliform results. If there are more dark pink/red colonies on the standard R-CARD® ECC test card than on the R-CARD® ECC-A, the differential indicates the presence and numbers of Aeromonas in the sample.
To enumerate, simply count the number of colonies of each type. Additionally, the pink/red colonies on the R-CARD® can be allowed to mature to the point at which any Aeromonas colonies are visible as faint yellow colonies that can easily be seen and counted.
The R-CARD® ECC-A Medium (Patent pending) eliminates the misreading of Aeromonas spp. as coliforms, a currently known issue with R-CARD® ECC and other products with similar formulations.
R-CARD® rapid tests offer a revolution in convenience without sacrificing accuracy. The cards are completely self-contained and don’t require petri dishes, agar, or other equipment that’s fragile and prone to leak. Simply place your sample on the card and wait 1-3 minutes for the liquid sample to solidify between the two layers. This prevents it from dripping or leaking. Cards can easily be carried in a coat or backpack pocket prior to incubation.
It’s also incredibly easy to read the R-CARD’s results. After the appropriate incubation time, simply count dark blue dots as the number of E. coli colonies, the pink/red dots as the number of coliform colonies, and any colorless or very light yellow colonies as Aeromonas spp. This easy-to-read color system is a significant improvement from other similar multi-bacteria tests, where differentiating among these three groups of microbes can be very difficult.
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