27-06-2012, 04:50 PM
Micro Biological analysis of drinking water
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The most common and widespread health risk associated with drinking water is
contamination; wither directly or indirectly, by human or animal excreta, particularly
faeces. If such contamination is recent, and if those responsible for it include carriers of
communicable enteric disease, some of the pathogenic microorganisms that cause these
diseases may be present in the water. Drinking the water, or using it in food preparation,
may then result in new cases of infection.
The pathogenic agents involved include bacteria, viruses, and protozoa, which may cause
diseases that vary in severity from mild gastroenteritis to severe and sometimes fatal
diarrhea, dysentery, hepatitis, or typhoid fever, most of them are widely distributed
throughout the world. Faecal contamination of drinking water is only one of several
faeco-oral mechanisms by which they can be transmitted from one person to another or,
in some cases, from animals to people.
Other pathogen cause infection when water containing them is used for bathing of for
recreation involving water contact, rather than by the oral route. Some may also cause
infection by inhalation when they are present in large numbers in water droplets, such as
those produced by showers and some air-conditioning systems or in the irrigation of
agricultural land.
Ideally, all samples taken from the distribution system including consumers’ premises
should be free from Coliforms organisms. In practice, this is not always attainable. To
control purity of water the following microbiological parameters for water collected in
the distribution system is therefore recommended.
Indian standard IS 1622 : 1981
a. Throughout any year, 95 % of samples should not contain any coliform
organisms in 100 ml.
b. No sample should contain E.Coli in 100 ml.
c. No sample should contain more than 10 coliform organisms per 100 ml.
d. Coliform organisms should not be detectable in 100 ml of any two
consecutive samples.
E.Coli
E.coli is a gram-negative, non-spore forming, rod-shaped bacterium which can be either
motile or nonmotile (motile cells are peritrichous); growth is aerobic or facultatively
anaerobic. Metabolism is both respiratory and fermentative; acid is produced by the
fermentation of glucose and lactose.
1. E.coli is found in large numbers in the faeces of humans and of nearly all warmblooded
animals; as such it serves as a reliable index of recent faecal
contamination of water.
2. E.Coli is abundant in human and animal faeces, in fresh faeces it may attain
concentrations of 109 per gram. It is found is sewage, treated effluents, and all
natural waters and soils subject to recent faecal contamination. Whether from
humans, wild animals, or agricultural activity.
3. E.Coli may be present or even multiply in tropical waters not subject to human
faecal pollution. However, even in the remotest regions, faecal contamination by
wild animals, including birds, can never be excluded, because animals can transmit
pathogens that are infective in humans, the presence of E.coli must not be ignored.
Total Coliform
The term “coliform organisms (total coliforms)” refers to gram negative, rod shaped
bacteria capable of growth in the presence of bile salts or other surface-active agents with
similar growth-inhibiting properties, and able to ferment lactose at 35 – 37oC with the
production of acid, gas, and aldehyde within 24 – 48 hours.
They are also oxidase-negative and non-spore-forming. These definitions have recently
been extended by the development of rapid and direct enzymatic methods for
enumerating and confirming members of the coliform group.
The existence both of non-faecal bacteria that fit the definitions of coliform bacteria and
of lactose-negative coliform bacteria limits the applicability of this group as an indicator
of faecal pollution.
The coliform test can therefore be used as an indicator both of treatment efficiency and of
the integrity of the integrity of the distribution system.
In our study for microbiological water quality we followed next methodology:
Sample collection procedure for Bacteriological analysis of drinking water.
1. Remove any attachment from the tap.
2. Using a clean cloth outlet of the tap wipe to remove any dirt.
3. Turn on the tap for maximum flow and the water may run for two minutes.
4. Outlet of the tap is sterilized by means of flame from cigarette lighter.
5. Tap again opened to flow for 1 to 2 minutes at medium flow rate.
6. Sterile 250 ml plastic bottle is taken for sample collection.
7. Carefully unscrew the cap and immediately hold the bottle under the water jet and
fill.
8. Water filled up to 200 ml and a small air space is left to make shaking before
analysis.
9. Collected sample delivered to laboratory within 20 to 30 minutes and inoculated
immediately.
Method for testing Total Coliform & E.coli
Name of the method: Multitube fermentation technique/MPN method
Presumption test:
1. Inoculated in 10 ml tubes containing Macconky broth and Durham tubes.
2. Tubes are kept in the incubator 37oC for 24 to 48 hours.
3. Any presence of bacteria will show gas production or colour change of the broth
from violet to yellow.
Conformation test for total coliform:
1. Inoculate from the positive tube from presumption test in Brilliant green broth
which contains Durham tubes.
2. The temperature is 37 + 0.50 C.
3. Presence of gas production confirm the presence of bacteria..
Conformational test for E.coli
1. Inoculate from the positive tube from presumption test in EC broth which
contains Durham tubes.
2. The temperature is 44 + 0.5o C.
3. Presence of gas production confirm the presence of bacteria.