Microbial Analysis of Water


The analysis of microbes in water is a key aspect of water quality that estimates the number of micro-organisms in water and if needed the type of micro-organisms. These microbes may be pathogenic to human beings.The analysis utilizes water samples from which the concentration of microbes is determined. The microbial analysis thus provides inferences for suitability of the water for consumption or any other use. This analytical procedure is crucial in preventing the spread of water-borne diseases that accounts for 3.4 million deaths per year according to the World Health Organisation (WHO). This procedure is performed by government agencies and water utilities to ensure a safe supply of water for drinking, swimming, domestic use and industrial use.

Principle of microbial analysis of water:

Regardless of methodology of the analysis the rationale is based on screening for indicator organisms rather than the pathogens that may cause concern. These indicator organisms are bacterial organisms such as fecal streptococci, non-specific coliforms, Escherichia coli and Pseudomonas that are commonly found in the human or animal gut, if detected they suggest presence of sewage in the water or contamination that brings with it pathogenic microbes. Indicator organisms are used in microbial analysis of water as their concentration are directly proportional to the concentration of more pathogenic microbes, that is to say that if the concentration of indicator organisms is high then it is assumed that the concentration of more pathogenic microbes is also high. However it may be necessarily to test the pathogenic organisms in some cases such microbial analysis of water in public drinking supplies that are tested for protozoan pathogen Cryptosporidium and Legionella species (both are water borne pathogens). Analysis can be biochemical, optical or use culture methods. Advanced techniques such as Molecular biology may be utilized when set reference ranges are exceeded.


All methods are based on statistical principles due to small sample size.

1) Multiple tube method: This method involves the dilution of a sub-sample with sterile growth medium and an aliquot of 10 ml is decanted in to each of the ten tubes. The remaining 10 ml is again diluted and the process repeated. In the end dilution of 1:10 to 1:10000 in 50 test tubes is achieved. The tubes are then incubated at a specific temperature and time. Growth in the tubes at different dilutions is then accounted for and the concentration is then derived using statistical tables

2) Membrane filtration method: A 10 ml sample is filtered through nominal pore size ranging from 0.2-0.45 um. The procedure is performed sceptically and a vacuum is utilized to draw sample through the filter.The process aims to filter out the microbes. They remain on filter and moved on to Petri dish with culture medium. The Petri dish is incubated at a specific temperature and time to allow for the replication of indicator organisms. colonies are counted in numbers as “colony forming units” of original sample.

3) Rapid techniques: The use of rapid tests particularly those utilizing Quantitative Polymerase chain reaction (QPCR) have shown competency both in the detection of indicator organisms such as E.coli and specific pathogens. A combination of membrane filtration and QPCR is a rapid and effective method in microbial analysis of water.

4) Culture techniques: These include pour and spread plate methods are useful in enumerating heterotrophic bacteria. They involve growth of the microbe on a culture media with subsequent enumeration of colonies to determine concentration.

5) ATP testing: This method quantifies active organisms through detection of Adenosine Triphosphate. The ATP is measured by measuring the light produced during a reaction with naturally occurring enzyme firefly luciferase using a luminometer.

Biofilm: Biofilms have been identified as complex microbial communities with a variety of bacterial species combined with exopolysacharides. This complexity is important in the growth of bacteria and helps bacteria to resist destruction by chlorine hence their importance in microbial analysis of water

Conclusion:The analysis of microbes in water is a vital component in water quality and ensures the protection of public health through the detection and quantification of pathogenic microbes.

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