1. MEMBRANE FILTRATION
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2. MEMBRANE FILTRATION 1. Filtration and Microscopy
eg. DEFT = Direct Epifluorescent Filter Technique
Uses:
originally to test hygienic quality of raw milk
now used to enumerate fresh and processed meat and fish, beverages and water supplies.
Technique:
sample filtered onto polycarbonate membrane
concentrates bacteria
stain with acridine orange
bacterial cells fluoresce and are counted under
epifluorescent microscope

3. MEMBRANE FILTRATION 2. Filtration and CFU determination
Use for raw products and in-process quality control
Concentrates relatively large volumes of sample eg liquid soft drink onto a membrane filter through a filtration manifold unit
Membrane filter is then aseptically removed onto a Nutrient Pad Set (sartorius)in a Petri dish and incubated
Nutrient pad is dehydrated culture media which has been rehydrated with sterile water
Colonies are counted after incubation

4. MEMBRANE FILTRATION
Sartorius supply nutrient pad sets with specialised selective media for microorganism detection in
Beer – especially sterility
Wine
Milk
Soft drink
Water
Food – largely as a pre-filter
(pharmaceuticals and cosmetics – especially testing drug sterility)

5. Filtration Flow Chart for Method of CFU determination (picture supplied by Sartorius)

6. How to use the nutrient pad sets for membrane filtration (picture supplied by Sartorius)

7. Total count on non-selective agar using a Nutrient Pad Set of mixed culture from water (picture supplied by Sartorius)

8. E. Coli and coliforms on chromocult Nutrient Pad Set of mixed culture from water (picture supplied by Sartorius)

9. Problems and Solutions
Difficulties filtering food suspensions
Helped by using a pre-filter usually made of glass fibre
Counting large number of colonies on a plate
Helped by using filters with hydrophobic grid lines. The lines are made of non-toxic water repellent material, so the colony size and spread is limited. (HGMF)