Coliform bacteria

Coliform is a group of bacteria which is found in human intestines. The presence of this bacteria in water indicates the contamination by disease causing microorganisms. It is rod shaped, Gm negative , non- spore producing bacteria which can ferment lactose with the production of acid and gas when it is incubated . It can be found in aquatic environment ,in soil and in vegetation . It is also present faeces of warm blooded animals and in intestine of humans. They are very easy to culture . Its high presence in rivers and ponds elevates the risks of water borne diseases like gastroenteritis .

Types of coliform bacteria -

Total coliform, fecal coliform, and E. coli are all indicators of drinking water quality . Fecal coliforms are types of total coliform that mostly exist in feces. E. coli is a sub-group of fecal coliform. When a water sample is sent to a lab, it is tested for total coliform. If total coliform is present, the sample will also be tested for either fecal coliform or E. coli, depending on the lab testing method.

1.Total coliform bacteria are commonly found in the environment (e.g., soil or vegetation) and are generally harmless. If only total coliform bacteria are detected in drinking water, the source is probably environmental. Fecal contamination is not likely.

2.Fecal coliform bacteria are a sub-group of total coliform bacteria. They appear in great quantities in the intestines and feces of people and animals. The presence of fecal coliform in a drinking water sample often indicates recent fecal contamination, meaning that there is a greater risk that pathogens are present than if only total coliform bacteria is detected.

3.E. coli is a sub-group of the fecal coliform group. Most E. coli bacteria are harmless and are found in great quantities in the intestines of people and warm-blooded animals. Some strains, however, can cause illness. The presence of E. coli in a drinking water sample almost always indicates recent fecal contamination, meaning there is a greater risk that pathogens are present.

                                             Image source credit -http://fppi.ca/bacteria-in-drinking-water/
Most coliform bacteria testing is performed via a “colorimetric” test. A colorimetric test is a test which forms a color. A distinctive color change indicates the presence of Total Coliform Bacteria. 

A testkit is used to reveal the presence of coli bacteria in potable water. The 

kit contains five glass tubes with growing media and shows a reliable 

indication about the presence of this pathogenic bacteria. 

This test is nor suitable for revealing other bacteria like legionella or hepatitis.

        Image source credit -https://www.amazon.com/Innovating-Science-Qualitative-Coliform-Tubes/dp/B00BUV7KFG


Q1.Coliform bacteria in water  is detected by
 -
a.Membrane filter method
b.Multiple tubule fermentation test
c . Both a and b
d.Direct streak method

Ans . c

Q2 . Which of the following coliform bacteria is found in contaminated water -

a.E.coli
b.Clostridium welchii
c.Streptococcus faecalis
d. All of the above

Ans . d

Q3.Coliform bacteria on fermentation of carbohydrates yields-

a.Lactic acid
b.Formic acid
c.Acetic acid
d.All of the above

Ans .d

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