Coliform Enumeration & Detection Water Tests | IHS Lab Hyderabad.
A. Background:
The usual source of waterborne pathogens is faecal contamination of human or animal origin. Waterborne pathogens include various microbial agents such as Vibrio cholerae, Salmonella (typhoid, paratyphoid), and Shigella dysenteriae. Direct identification of pathogens in water requires many time-consuming test procedures and is operationally infeasible for water supply authorities. To overcome these difficulties, coliforms are identified as indicators of microbial contamination because their culture and identification are operationally feasible.
Water borne pathogens include various microbial agent such as; Vibrio cholerae, Salmonella (typhoid, paratyphoid), Shigella dysenteriae, Hepatitis virus, etc. Direct identification of all water borne pathogens is complex, time consuming and expensive. Instead, looking for organisms that indicate faecal contamination provides a feasible and cost-effective alternative. Members of two bacteria groups, coliforms and fecal streptococci, are used as indicators of possible sewage contamination because they are commonly found in human and animal feces. Although they are generally not harmful themselves, they indicate the possible presence of disease-causing bacteria, viruses, and protozoans that also live in human and animal digestive systems.
The coliform tests are based on culture of indicator bacteria to identify faecal contamination. Total coliforms are found everywhere. All members of the total coliform group can occur in human feces, but some can also be present in animal manure, soil, and submerged wood and in other places outside the human body. A subset of total coliforms that can survive and grow at relatively higher temperatures are called thermotolerant coliforms (TTC). Most thermotolerant coliforms inhabit the intestinal tract of man and animals in great abundance and hence are also known as faecal coliforms (FC). However, this group includes a genus such as Klebsiella, which is not necessarily of faecal origin. E. coli, which is a thermotolerant coliform is specific to fecal material from humans and other warm-blooded animals. Thus, while faecal coliforms are useful indicators of sewage contamination, presence of E. coli is a more specific indicator of faecal contamination. Hence detection of E. coli is a definite indicator of faecal contamination.
Coliform tests are cost-effective solution to rule out (or identify) faecal contamination of water. Water utilities all over the world rely on coliform tests to monitor water quality. The World Health Organization (WHO) recommends coliform bacteria as useful indicators for assurance of drinking water quality. Presence of E. coli is an indicator of contamination with human sewage. Total coliforms in the absence of E. coli) would be an indicator for cleanliness and integrity of distribution systems (WHO, 2011). The Indian Standard Drinking Water Specification requires that, in respect of all water intended for drinking, E. coli shall not be detectable in any 100 ml sample (IS10500, 2012).
B. MPN - MTF Methods:
MPN (Total Coliforms) is a targeted group test to estimate density of lactose-fermenting coliform bacteria. Because coliforms originate both in the natural environment and the intestines of warm-blooded animals, the coliform test specifically flags sanitary breaches, treatment failures, or potential fecal contamination. Total coliforms are not naturally present in deep borewell or unpolluted groundwater. Their detection usually means the existence of pathway(s) for mixing of water carrying coliforms from the environment and conditions nurturing further growth in the recipient water body.
The MPN(TC) serves as a critical indicator for assessing the sanitary conditions of ambient water bodies (such as rivers, lakes, and groundwater), evaluating water treatment efficiency, and monitoring the cleanliness and integrity of intermediate storages, distribution networks, and finished drinking water. However, MPN(TC) test results should be interpreted cautiously because many environmental coliforms thrive naturally in surface water bodies and untreated supplies. While MPN(TC) is useful as an operational indicator for monitoring of treatment systems, additional tests for the detection/enumeration of fecal coliforms and E. coli are required to assess the microbial safety of water. Consequently, water quality regulatory frameworks often use total coliform thresholds to trigger systemic reassessment rather than to signal an imminent health violation.
Faecal coliforms, more appropriately called thermotolerant coliforms, are a subset of total coliforms that naturally live in the bowels of humans and warm-blooded animals. They are identified in the laboratory by their ability to ferment lactose and grow at an elevated temperature of 44.5°C. As they originate from animal and human excreta (such as cow dung, bird droppings, and sewage), their density—frequently measured as the Most Probable Number [MPN(FC)]— indicates potential exposure to microbial pathogens. Because some thermotolerant coliforms can also originate from non-faecal environments (such as industrial effluents or plant matter), MPN(FC) is considered a strong but presumptive indicator of faecal pollution. Consequently, Escherichia coli (E. coli) is often tested alongside or instead of total thermotolerant coliforms for definitive confirmation.
Escherichia coli (E. coli) is a subset of thermotolerant coliforms. Most E. coli strains are harmless commensals that inhabit a healthy intestinal tract and find their way into excreta. Since these bacteria originate in the intestines of warm-blooded organisms and do not ordinarily survive for long in the environment, their presence in water bodies and groundwater is a key indicator of recent faecal contamination. However, in tropical climates there is a very small chance of certain naturalized strains to persist in soils and sediments. Even if environmental persistence is possible, regulatory and public health bodies always treat the presence of E. coli as proof of a structural vulnerability or pathway to fecal pollution until proven otherwise.
Coliform tests have evolved from the classic Most Probable Number (MPN) Multiple-Tube Fermentation to Membrane Filtration & Culture (MFC) and Enzyme Substrate Analysis (ESA) methods. MPN/MTF is better at recovering injured or stressed coliforms because of the initial liquid pre-enrichment, serial dilution matrix and statistical estimation, but is labour intensive and time consuming. Turbid samples can be processed by MPN/MTF method. As the MPN range of the baseline MPN test matrix is higher [up to >1600 (IS1622:2026)] results can be used to differentiate severity of pollution in water bodies. On the other hand, MFC and ESA provide comparable accuracy for clear water, require less effort and yield faster results. Consequently, the selection of test method that is appropriate for the source and purpose is key to the correct interpretation of test results.
Accordingly, the MPN/MTF method is recommended in the following scenarios:
- Surface water bodies for baseline compliance monitoring and to differentiate severity of pollution;
- ii. Sources with high suspended solids or algae such as fish/livestock ponds, storm runoffs, lakes and rivers; and
- Wastewater, raw sewage, sewage treatment plant effluents and industrial process waters where coliform concentrations are expected to be high.
Note that the MPN values reported in any MPN-MTF test is a statistical estimate per 100ml derived from analysis of 55.5ml sample configured in serial dilutions as per IS 1622:2026. This does not satisfy the requirement of IS 10500 which explicitly requires that E. coli or thermotolerant (faecal) coliforms shall not be detectable in any 100 ml sample.
Following coliform enumeration test codes of IHS Laboratory meet the requirement of IS 10500 drinking water specification:
-------------
To pick up sample collection bottle and/or schedule collection of samples: Email: ihslab@ihs.org.in with your address and contact telephone; OR WhatsApp: +919848011251; Or Call: 23211013/4.