Water Sampling Methods

1-Membrane filtration method2-Pour plate method3-Spread plate method4-Multiple tube method5-ATP testing method

There are different water sampling methods.

Requirements:Filtration assemblyMembrane filter(nominal pore size 0.2 or

0.45mm).Vacuum pumpSample

1-Membrane filtration method

In the membrane-filtration (MF) method, a minimum volume of 10 ml of the sample (or dilution of the sample) is taken.

Introduced aseptically into a sterile or properly disinfected filtration assembly containing a sterile membrane filter (nominal pore size 0.2 or 0.45mm).

A vacuum is applied and the sample is drawn through the membrane filter.

Procedure

All indicator organisms are retained on or within the filter, which is then transferred to a suitable selective culture medium in a Petri dish.

Petri dish is transferred to an incubator at the appropriate selective temperature where it is incubated for a suitable time to allow the replication of the indicator organisms.

Visually identifiable colonies are formed and counted, and the results are expressed in numbers of “colony forming units” (CFU) per 100 ml of original sample.

Results

Both methods are same but with few differences.In both the methods serial dilutions of the sample

is used.

2-Pour plate method 3-Spread plate method

From each serial dilution culture is prepared but in pour plate method two types of colonies are obtained surface and sub-surface as compared to spread plate method.

In pour plate method both agar and sample are poured together and are mixed thoroughly.

While in spread plate method sample is spread on agar.

After all the pouring and spreading petri dishes are incubated at 37°c for 24 hrs.

After incubation colonies are obtained and counted with naked eye.

Result

The multiple-tube method is also referred to as the most probable number(MPN) method.

Aim:Total or presumptive coliform count.Confirmed coliform and ecoli count.Requirements:Sterile bottleMacConkey’s broth with bromocresol purple.Brilliant green bile lactose broth.Tryptone water.Test tubes.

Multiple tube method

MacConkey’s broth:Make 50ml double strength M.BPour 10ml double strength M.B in 5 test

tubes.Pour 5ml single strength M.B in 5 test tubes.Each tube has durham’s tube.Autoclave the prepared meida.

Media preparation

Take sterilized bottle of 100 ml with 0.1ml of 1.8% sodium thiosulphate.

Flame the mouth of tape and bottle before sample collection.

Let the water running for2-3 minutes then collect sampl.

cap the bottle and thoroughly mix the water.

Sample collection

Pour 50ml sample in 50ml double strength M.B

5ml sample in each 5 tubes with double strength M.B.

1ml sample to each 5 test tubes with single strength M.B.

Then incubate all the tubes at 37°c for 18-24 hrs.

Procedure

After incubation observe those tubes with acid and gas production.

These tubes will give presumptive coliform count.

it is based on an indirect assessment of microbial density in the water sample by reference to statistical tables to determine the most probable number of microorganisms present in the original sample.

Results

The concentration of microorganisms in the original sample can then be estimated from the pattern of positive results (the number of tubes showing growth in each volume series) by means of statistical tables that give the “most probable number” per 100 ml of the original sample.