MEMBRANE FILTRATION
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reproduced with permission from the
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producing the respective products.
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 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
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
membran
e 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)