2
Introduction
8
A vacuum hand pump attached to the MFU
creates suction that pulls the sample water
through a sterile membrane filter that sits in
place in the MFU.
This membrane filter has small pores in it that
allow the water to pass through easily but any
bacteria present in the water are trapped on the
surface of the filter membrane.
This filter is then removed and placed carefully
onto an absorbent pad that sits in the base of
a sterile petri dish.
The absorbent pad has been soaked in a liquid
culture medium which provides nutrients for
bacteria to grow whilst at the same time
inhibiting growth of any non-target bacteria.
The petri dish is then placed in the portable
incubator included in the Potalab
®
+ (M) kits.
The temperature can be set to either 37 or 44ºC,
allowing the user to carry out tests for Total or
Faecal (Thermotolerant) Coliforms.
The petri dishes are incubated for a minimum
of 14 hours at optimum growth temperatures.
During this period the Coliform bacteria will
multiply rapidly to form colonies that are visible
to the naked eye.
Coliforms are identified by their ability to cause
a colour change in the growth media when
incubated. They will show up as yellow in colour
against the red/pink background of the media.
The yellow colonies are counted and the results
expressed as Colony Forming Units per 100ml
of water - CFU/100ml (assuming sample size
was 100ml).
Useful to Know
• Always wash your hands before
carrying out your microbiological
analysis, and again after handling
potentially contaminated materials
• Never eat or drink while carrying
out a microbiological test
• Never smoke while carrying out a
microbiological test
• Do not directly touch any colonies
in the petri dish
• Always hold the petri dishes by the sides
and keep the lid on whenever possible
• Try to ensure that your workspace is clean
and tidy - disinfect if possible (methanol)
• Ensure all open wounds are
covered adequately
• Always sterilise the materials from the
test before disposal and do not dispose
of potentially contaminated materials
directly into the environment
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