3
Preparation
12
3.6 Preparing Culture Media in the Field
using the Media Measuring Device (MMD)
Items Required:
• 38.1g Membrane Lauryl Sulphate Broth (MLSB)
• Media Measuring Device (MMD)
• 100ml distilled or clean water
• pH Meter
• Pressure Cooker/Steriliser/Autoclave
• Heat Source
1 If no distilled water is available, choose the
cleanest water available e.g. rainwater, filtered
water, or, if necessary, stand raw water in a
container overnight. Do not use water which has
been chlorinated. Boil the water for at least ten
minutes, cover and allow it to cool down.
2 If using raw water then it may be necessary to
filter 100ml of this water through the membrane
filter using the membrane filtration unit (MFU) -
see Section 7 MFU Operation. If the water is
turbid, this step may need to be repeated.
Prepare as much filtered water as you require.
3 Use the pH Meter to check the pH of water to be
used to make up the liquid media. To make up
MLSB the water should be pH 7.2 - 7.6. pH must
be corrected or an alternative source of water
will need to be found if the value is outside of
the ideal range. Adjust the pH by using dilute
sodium hydroxide solution (increases pH) or
dilute hydrochloric acid (reduces pH).
4 Boil the distilled/clean water for 10 minutes
and then allow it to cool.
5 Ensure that the MMD are sterile before
beginning. MMDs can be sterilised upright
using an autoclave. Screw on the lid so that it is
secure but not completely air tight to prevent high
pressure developing. Take care not to place the
MMD directly onto the base of the autoclave.
Sterilise at 121°C for 10 minutes. Alternatively,
place MMD in a pressure cooker and maintain
steam at pressure for 15 minutes.
6 Remove the MMD, allow to cool.
7 Once cool, unscrew the blue lid/spoon of
the
MMD. Take ten level spoonfuls of media
from the
38.1g container of the MLSB and
add to the
MMD. Always hold via the lid and do not
touch the spoon itself.
8 Fill the MMD with sterilised water to the
lower lip and screw the lid on tightly.
9 Shake the MMD
to aid dissolving
of the powdered
MLSB. Once
dissolved a
bright red/pink
liquid will be
produced.
10 Ideally, to minimise the risk of contamination,
the MMD containing the
liquid MLSB should
now be sterilised. Undo the lid slightly so that it
is secure but slightly
loose and sterilise again
as in Step 5.
11 Upon completion, remove the MMD and allow
to cool. Tighten the tops securely and store in
a cool, dark place until ready to use.
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