8
2
Introduction
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
Potatest
TM
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
