- Collect the sample and make any necessary dilutions.
- Select the appropriate nutrient or culture medium. Dispense the broth into a sterile Petri dish, evenly saturating the absorbent pad.
- Flame the forceps, and remove the membrane from the sterile package.
- Place the membrane filter into the funnel assembly.
- Flame the pouring lip of the sample container and pour the sample into the funnel.
- Turn on the vacuum and allow the sample to draw completely through the filter.
- Rinse funnel with sterile buffered water. Turn on vacuum and allow the liquid to draw completely through the filter.
- Flame the forceps and remove the membrane filter from the funnel.
- Place the membrane filter into the prepared Petri dish.
- Incubate at the proper temperature and for the appropriate time period.
- Count and confirm the colonies and report the results.
Advantage of Membrane Filter Technique
- Permits testing of large sample volumes. Theoretically almost any volumes of nontubrid water could be filtered through the disk, the organisms from any given volume being deposited in the disk.
- The membrane can be transferred from one medium to another for purposes of selection or differentiation of organisms thus allowing isolation and enumeration of discrete colonies of bacteria.
- Results can be obtained more rapidly than by the conventional MPN standard methods. It provides presence or absence information within 24 hours.
Uses of Memberane filters
- Membrane filters are used extensively in the laboratory and in industry to sterilize heat labile fluid materials.
- Effective and acceptable technique to monitor drinking water.
- Useful for bacterial monitoring in the pharmaceutical, cosmetics, electronics, and food and beverage industries.
- Allows for removal of bacteriostatic or cidal agents that would not be removed in pour plate, spread plate, or MPN techniques.