Membrane Filtration of Water
Experiment No: 5 Membrane Filtration Method in “Basic methods for the Microbiological Analysis of Foods” by Prof. Dr. Osman ERKMEN. Nobel Yayınevi. Ankara 2007.
1- Dirty river water (100, 150, 200 ml)
2- Drinking water (100, 150, 200 ml)
1- Membrane Filtration Apparatus and Vacuum pump.
2- Plate Count Agar.
3- Sterile filter paper (0.45 mm)
1- First Sterilize the Filtration apparatus and forceps by passing through flame.
2- Place the coarse filter between flask and funnel and close the lid. Make sure the tap of funnel is closed.
3- Take 50ml of water sample and pour into funnel without filter paper to make a trial run to wet the surface of coarse filter. Run the vacuum pump and open the tap of funnel.
4- All of the sample should be passed through coarse filter.
5- Release the funnel lock and take a sterile filter paper.
6- Open the package of filter paper at aseptic conditions and take it by using sterile forceps.
7- Place the filter paper on the coarse (green side upper) filter let it get wet and remove the green upper cover by using forceps. Filter paper should be stick on the surface of coarse filter.
8- Then place the funnel close the lock. Close the tap of funnel.
9- Add 100 ml of sample in the funnel at aseptic conditions and run the vacuum pump. Open the tap of funnel to pass the entire sample through the filter paper.
10- After all of the sample was passed, remove the funnel and remove the filter paper from the surface of coarse filter.
11- Place the filter paper on PCA at aseptic conditions. And close the lid of petri dish.
12- Repeat the procedure for 150, 200 ml of sample amounts.
13- Incubate the petri dishes in the 37°C Incubator.
14- Count formed colonies on the filter paper. Calculate number of microorganisms per ml of water sample.
Membrane filtration systems are especially used when the sample like drinking water or fruit j uices which can easily pass through the filter and contain really small amount of microorganisms less than 1 CFU/ ml.
About coliform bacteria and why do we do this test:
Coliform bacteria are present in the environment and feces of all warm-blooded animals and humans. Coliform bacteria are unlikely to cause illness. However, their presence in drinking water indicates that disease-causing organisms (pathogens) could be in the water system. Most pathogens that can contaminate water supplies come from the feces of humans or animals. Testing drinking water for all possible pathogens is complex, time-consuming, and expensive. It is easy and inexpensive to test for coliform bacteria. If testing detects coliform bacteria in a water sample, water services search for the source of contamination and restore safe drinking water. There are three groups of coliform bacteria. Each is an indicator of drinking water quality and each has a different level of risk. Total coliform is a large collection of different kinds of bacteria. Fecal coliform are types of total coliform that exist in feces. E. coli is a subgroup of fecal coliform. Labs test drinking water samples for total coliform. If total coliform is present, the lab also tests the sample for fecal coliform or E. coli, depending on the lab testing method. Total coliform bacteria are common in the environment (soil or vegetation) and are generally harmless. If a lab detects only total coliform bacteria in drinking water, the source is probably environmental and fecal contamination is unlikely. However, if environmental contamination can enter the system, pathogens could get in, too. It is important to find and resolve the source of the contamination. Fecal coliform bacteria are a subgroup of total coliform bacteria. They exist in the intestines and feces of people and animals. The presence of fecal coliform in a drinking water sample often indicates recent fecal contamination. That means there is a greater risk that pathogens are present. E. coli is a subgroup of the fecal coliform group. Most E. coli bacteria are harmless and exist in the intestines of people and warm-blooded animals. However, some strains can cause illness. The presence of E. coli in a drinking water sample usually indicates recent fecal contamination. That means there is a greater risk that pathogens are present. Note: E. coli outbreaks receive a lot of media coverage. A specific strain of E. coli bacteria known as E. coli O157:H7 causes most of those outbreaks. When a drinking water sample is reported as “E. coli present,” it does not mean that O157:H7 is present. However, it does indicate recent fecal contamination. Boiling or disinfecting contaminated drinking water destroys all forms of E. coli, including O157:H7.