12
3
Preparation
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.
