19 Use the sterile forceps to remove the
membrane filter from the filtration unit.
20 Starting at the far edge of the petri dish, use
a rolling motion to place the membrane filter
on top of the absorbent pad. This will prevent
air being trapped between the pad and
membrane filter.
21 Replace the petri dish lid and label with
sample number, place, date, time, etc. to
identify in the rack.
22 Place the petri dish into the petri dish rack and
repeat the process for all samples. Place the
filled rack into the incubator for safe storage
ready to start the incubation.
Ensure that the incubator is in the upright
position at all times to avoid leakage of
nutrient broth from petri dishes, paying
particular attention when transporting.
5.1 Resuscitation Period
It is important to note that when the last sample
has been processed, a resuscitation period of
between one and four hours must be observed
before incubation commences.
Environmental exposure can cause coliforms to
become physiologically stressed. The resuscitation
period allows coliforms to recover before culturing.
With this in mind it is essential to plan testing
throughout the day, particularly if visiting multiple
sample sites. Try to conduct all sample processing
within a three hour window. This ensures a
maximum resuscitation period of four hours.
The resuscitation period is especially relevant for
water samples where the environmental exposure
is due to chlorination.
The incubator operating software includes the
capacity to have an initial resuscitation period as
part of the standard incubation cycle.
5.2 Incubation Time
Incubate the samples for 18 hours at the desired
temperature. Two preset incubation
profiles are
available on the Wagtech Incubator:
• To test for Total Coliforms incubate at 37ºC
for 18 hours
• To test for Thermotolerant Coliforms incubate
at 44ºC for 18 hours
19
5
Sample Processing - Membrane Filtration
Useful to Know
• It is preferable to run the incubator
in-situ in the case
• Ensure the incubator lid is closed
• If powering from the battery only,
ensure the case lid is closed to minimise
power consumption
• Do not place the kit directly on the
floor during incubation
• Do not incubate outdoors during
periods of cold temperature
• Ensure that the petri dish rack is full
during incubation, using empty dishes,
to allow even heat distribution
• After switching on the incubator and
selecting the desired temperature, allow
a few minutes for the set-point to be
reached and for temperature to stabilise.
The incubator will show ‘warming up’ for
a period of 30 minutes
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