[ExpertScie]

There are various methods which are employed in microbial evaluation of water: Few of them are aligned with today’s modern technology and few are based fundamental microbiological concepts.

1)ATP Testing:
In this method, detection of Adenosine Triphosphate or ATP is done and this helps to rapidly measure active microorganism in water. The Principle of this testing is that ATP molecule is found only in and around living cell and therefore such measure will be directly related to the biological concentration. Further this measure is classified depending upon the type of life. The ATP is quantified by measuring the light produced through its reaction with the firefly enzyme Luciferase using Luminometer.

2)Multiple Tube Method :
This method is based on fundamental concept of microbiology. This is one of the oldest methods.
In this method, the measured sub-sample is diluted for example the 10ml sample is diluted with 100 ml sterile growth medium. Further, aliquot of 10ml is decanted into each of the tubes. Such way, the dilution range of 1:10 through to 1:10000 is produced. After incubation, the number of tubes with growth is counted for each dilution. The standard calibration plot or standard table is then referred to know the concentration of organism in the original test sample.

3) Membrane Filtration:
The serially diluted samples are vacuum filtered through membrane filters and these filters are then laid on growth media like nutrient agar. Membranes have a printed millimeter grid on and can be reliably count.

Such methods help in microbiological evaluation of water and can conclude on the type and its suitability.