Detection and Enumeration of Coliforms in Ganga Water
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The document details an investigation of coliform bacteria in Ganga water from various ghats using the Most Probable Number (MPN) method. Results indicated that all water samples were unsafe, primarily contaminated with Escherichia coliforms, alongside other species like Klebsiella and Enterobacter. Additional findings suggest that coliform presence may signal failures in water treatment, with the number of bacteria varying based on environmental temperature.
Detection and Enumeration of Coliforms in Ganga Water
- 1. DETECTION AND ENUMERATION OF COLIFORMS IN GANGA WATER COLLECTD FROM DIFFERENT GHATS Submitted by TUHIN SAMANTA
- 2. INTRODUCTION Most probable number (MPN) analysis is a statistical method based on the random dispersion of microorganisms per volume in a given sample. In this method, measured volumes of water is added to a series of tube containing a liquid indicator growth medium. The media receiving one or more indicator bacteria show growth and a characteristic color change. Color change is absent in those receiving an inoculums of water without indicator bacteria.
- 3. OBJECTIVES • To check the bacteriological quality of Ganga water at different Ghats. • To enumerate the number of bacteria present in the drinking water by MPN method. • To identify the bacteria present in the drinking water sample. • To differentiate various coliforms in water sample.
- 4. METHOD Method used for the investigation of coliforms is MPN method. The MPN values for coliforms range between 280 and 1600/100 ml. MPN test is completed in three steps:- Presumptive test Confirmed test Completed test
- 5. • Advantages of MPN • Ease of interpretation, either by observation or gas emission • Sample toxins are diluted • Effective method of analyzing highly turbid samples such as sediments, sludge, mud, etc. • that cannot be analyzed by membrane filtration. • Disadvantages of MPN • It takes a long time to get the results • Results are not very accurate • Requires more hardware (glassware) and media • Probability of false positives
- 6. PRESUMPTIVE TEST It is used for detection and estimation of coliform in water sample. For estimation of coliforms, lactose containing broth medium is used. Commonly used medium is MacConkey broth that contains the indicator bromocresol purple. An inverted Durham’s tube is placed. The color of media changes into yellow and on collection of gas in Durham's tube, bacteria are assumed to be coliform. Number of positive tubes are counted and referred to the standard chart to find MPN of total 100 ml water sample.
- 7. CONFIRMED TEST Some spore forming bacteria give false positive test in presumptive test. Confirmed test is done to determine that the coliforms are of fecal origin or not. And they are E. coli or not. For this positive presumptive test are inoculated in selective media like Eosine Methylene Blue (EMB) agar and incubated at 44.5°Cand 37°C. Presence of typical colonies at 37°C confirms positive coliform test and those at 44.5°C confirms the presence of E. coli.
- 8. COMPLETED TEST Subculture typical colonies in lactose containing medium and incubated at 37° C and 44.5 °C. Presence of E. coli is confirmed by the production of gas at 44.5 °C.
- 9. CONCLUSION According to MPN for detection of coliforms, all water sample collected from different Ghats were unsafe. The water was mainly contaminated by coliform bacteria Escherichia, followed by Klebsiella, Enterobacter and Citrobacter. Twenty nine different species were identified from ten different samples. Variation of coliforms occurrence is entirely dependent on temperature. The presence of coliform bacteria in treated drinking water may indicate the failure of treatment.
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