MPN is most generally applied for quality testing of water i.e to guarantee whether the water is protected or not as far as microorganisms present in it. A gathering of microscopic organisms normally alluded as fecal coliforms go about as a pointer for fecal pollution of water. The nearness of not many fecal coliform microbes would show that a water presumably contains no disease‑causing living beings, while the nearness of huge quantities of fecal coliform microscopic organisms would demonstrate an extremely high likelihood that the water could contain disease‑producing life forms making the water hazardous for utilization.

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.

10. REFERENCES
• Ahmed, T., et al. 2013. Microbiological study of drinking water: Qualitative and
quantitative approach. Asian J. Microbiol. Biotech. Env. Sc. 15 (4). 647-654.
• Acharjee, M., F. Jahan, F. Rahman, and R. Noor. 2013. Bacterial proliferation in
municipal water supplied in Mirpur locality of Dhaka City, Bangladesh. Clean – Soil,
Air, Water. 41. 1-8.
• Haq, A. K. 2006. Water management in Dhaka. Water Resource Development. 22 (2).
291-311.
• Mead, A. M., G. Helm, P. Callan, and R. M. Atlas. 1999. A prospective study of drinking
water quality and gastrointestinal diseases. New Eng. J. Med. 245 (9). 224-248.
• Kamal, M. M. A., M. Hansen and A. B. M. Badruzzaman. 1999. Assessment of pollution
of the river Buriganga, using a water quality model. Water Sci. Tech. 40 (2). 129-136.