English: Membrane filtration

Procedures:

1. 15 ml of liquid mFC agar and mEndo agar are to be poured in sterile plates and allowed to solidify.

2. The membrane filtration system is assembled accordingly: a receptacle is placed at the base and connected to a pump. The filter funnel should be placed next on the receptacle. Using sterile pincers a sterile membrane filter is to be placed on top of the filter funnel before placing the previously sterilized funnel on top. Clamping the funnel must be done carefully as to not displace the centrally placed filter.

3. 100 ml of the water sample are to be transferred in the funnel. The funnel lid should be placed to prevent organic or inorganic contamination of the water sample.

4. Once the apparatus and the sample are in place, the vacuum pump may be turned on and allowed to persist for a while once the full content has passed through the filter. Then it may be turned off or kept on depending on preference and technical capabilities.

5. The clamp and the funnel are to be disassembled before using sterile pincers to transfer the membrane filter onto a plate of the previously solidified medium.

6. The step above is to be repeated for each previously prepared plate.

7. Incubation is to be carried out at 37 ^оС for 24 hours for total coliforms and 44.5 ^оС for 24 hours for faecal coliforms.

RESULTS: Coliform colonies should show a distinct red or rose color on the mEndo plates with a light metallic greenish-red glaze. Colonies without the metalic glaze are not to be considered as coliforms. mFC plates are to be interpreted identically. Faecal coliforms will show up as blue colonies with no glaze.

Planned and performed by Sofija Kostandinovska, Institute of Biology, FNSM, Ss. Cyril and Methodius University, Skopje, Macedonia.