MEMBRANE FILTRATION

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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

MEMBRANE FILTRATION2. 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

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)

Filtration Flow Chart

for Method of CFU

determination(picture

supplied by Sartorius)

How to use the nutrient pad sets

for membrane filtration

(picture supplied

by Sartorius)

Total count on non-selective agar using a Nutrient Pad Set of mixed culture from water

(picture supplied by Sartorius)

E. Coli and coliforms on chromocult Nutrient Pad Set of mixed culture from

water (picture supplied by Sartorius)

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)