Description
Membrane Filters
Membrane filters are constructed out of a wide range of synthetic materials, including cellulose acetate, cellulose nitrate (collodion), polyamide (nylon), polycarbonate, polypropylene, and polytetrafluoroethylene (Teflon). In industries like pharmaceuticals, cosmetics, food and beverages etc. the membrane filters are used to monitor the presence of bacteria. Besides this, membrane filters are extensively used in water engineering to analyse the quality of water by the direct microbial count.
What membrane filters are used for Microbiology?
Individually wrapped sterile membrane filters can be used for Colony Counting, Sterility Testing, Microscopy and Particle Testing. The Gridded Membrane Filter enables easier colony counting. Membrane Filters used in microbiology and made from cellulose acetate or cellulose nitrate (collodion).
MEMBRANE FILTER TEST
The MF test is easier to perform than the MPN test because it requires fewer test tubes and less handling. Usually about 100 ml of water is passed through a membrane filter (pore size 0.45 µm). This membrane is then placed on a thin, absorbent pad saturated with differential or selective medium (Figure 17.2). For example, if total coliform organisms are sought, a modified Endo medium is used. For coliform bacteria, the filter is incubated at 35 ° C for 18 to 24 hours. The success of the method depends on using the correct media to facilitate identification of the bacterial colonies growing on the membrane filter surface. To continue with the previous example, enumerating colonies that have a green sheen indicates the number of coliform bacteria in a water sample.
C.P. GERBA, I.L. PEPPER, in Environmental Monitoring and Characterization, 2004
FIGURE 17.2. Membrane filtration for determining the coliform count in a water sample, using vacuum filtration (From Pollution Science © 1996, Academic Press, San Diego.)
Selection of appropriate nutrient medium: For the isolation and enumeration of different pathogenic microorganisms in water, we can use a variety of nutrient medium.
| Microorganisms in water | Nutrient medium used |
|---|---|
| Total coliforms | MF- Endo |
| Fecal coliforms | M- FC |
| Yeast and Molds | M- Green YM |
| Total bacteria | M- TGE / Trypticase Soy USP |
| Fecal streptococci | KF- Streptococcal |
| Lactobacillus acid resistant bacteria | Orange serum |
