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ColiMinder Measurement Approach

Microbiological contamination, most important water quality parameter, still evaluated manually by a 1-3 days lab procedure which is not suitable for automation, online monitoring and process control. ColiMinder technology is based on direct measurement of specific metabolic (enzymatic) activity of target organisms present in the sample.


The technology is extremely robust, directly linked to living organisms and suitable for all applications. Enzymatic activity is scientifically defined exactly

Enzymatic Evaluation

The enzymatic approach directly measures the specific enzymatic activity present in the sample. The measured enzymatic activity per sample volume is used as a measure of the contamination.

The enzymatic measurement approach is the only rapid measurement approach that allowsThe enzymatic measurement approach is the only rapid measurement approach that allows

  • Technology independent determination if contamination limits
  • Calibration of devices independent of their measurement technology

Both conditions are a prerequisite for a future standardization. The enzymatic approach is not limited to water – is it possible to measure other liquids, surface-contamination and air/gas also.

Standard Lab Evaluation

The classic laboratory method uses the proliferation of bacteria to make them visible in order to count them. The number of colonies formed per sample volume is used as a mesure of the degree of contamination.”

Indicator Bacteria

By comparing different measurement approaches, it is important to understand the principle of indicator bacteria. E. coli, Enterococci and Total Activity (ALP) are used as indicators of fecal and microbiological contamination. The higher the contamination, the higher the risk of pathogens and all kinds of infectious germs that spread through the metabolic pathway. For this reason, water is generally tested for E. coli and others.

The question to be answered by testing for indicator bacteria is:

How high is the level of fecal contamination of a sample? – because this indicates the level of risk

The classical method to evaluate the level of contamination is utilizing the growth of bacteria (E. coli, Enterococci or HPC) as a measurement instrument, and the number of colonies formed, to determine the level of contamination. The ColiMinder® is using the metabolic activity of target organisms “specific enzymatic activity) present in the sample, as a measure for how many living target organisms are present per sample volume, to determine the level of contamination and risk.

Scientific Definition of enzymatic activity

One important fact may be mentioned here: enzymatic activity, for example the E. coli specific ß-Glucuronidase activity, is scientifically exactly defined.

An exact scientific definition of ß-Glucuronidase is given in Modified Fishman Units:

GUS / E.coli specific enzymatic activity

MFU (Modified Fishman Unit): One MFU will liberate 1.0 μg of phenolphthalein from phenolphthalein glucuronide per hour at pH 6.8 at 37°C.

As a direct consequence VWM´s ColiMinder® is calibrated and delivering a result on E. coli contamination in Modified Fishman Units per Volume, representing E. coli -specific enzymatic activity per volume of sample as a direct measure representing the number of living organisms per sample volume. As the measurement parameter of enzymatic activity is scientifically exactly defined it provides the base to adopt respective limits of tolerable contamination expressed in enzymatic activity, for all kinds of applications.

GLU / Enterococcus specific enzymatic activity :

Beta-D-Glucosidase (EC, CAS 9001-22-3) is measured in “GU (Glucosidase Units)”. Unit Definition: One GU (Glucosidase Unit) liberate 1.0 µmole of p-nitrophenol (pNP) from p-nitrophenyl-β-D-glucopyranoside (10 mM) per minute in 50 mM sodium maleate buffer, pH 6.5 at 40°C (5).

ALP / total enzymatic activity:

Alkaline Phosphatase (EC, CAS 9001-78-9) is measured in “U (Units)”. Unit Definition: One U (Unit) hydrolyze 1.0 µmol p-nitrophenyl phosphate (6 mM) per minute in 87 mM glycine buffer, containing 0.9 mM MgCl2 and 0.87 mM ZnCl2, pH 10.4 at 37°C (6).

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