palintest Wagtech Potatest + Manual page 7

Total Coliforms refers to a large group of
Gram-negative, rod-shaped bacteria that share
several characteristics. The group includes
Thermotolerant Coliforms and bacteria of
faecal origin, as well as some bacteria that
may be isolated from environmental sources.
Thus the presence of Total Coliforms may or
may not indicate faecal contamination. In
extreme cases a high count for the Total
Coliform group may be associated with a
low, or even zero, count for Thermotolerant
Coliforms. Such a result would not necessarily
indicate the presence of faecal contamination.
It may be caused by entry of soil or organic
matter into the water or by conditions suitable
for the growth of other types of coliform
bacteria. Generally, Total Coliforms are grown
in or on a medium containing lactose at a
temperature of 35 or 37°C.
Carrying out microbiological analysis of
this sort therefore presents certain risks as
it is highly likely that you will be handling
equipment and materials that are potentially
contaminated with harmful pathogens. This
is especially relevant for the filter membranes,
absorbent pads and petri dishes that are
used in the test. For these reasons, general
hygiene and aseptic procedures are of
paramount importance and extra care
must be taken when working in the field.
2.1.2 Overview of the Procedure
for the Microbiological Analysis
of Drinking Water
The Wagtech kits use classical laboratory
techniques and equipment that have been
adapted for use in the field. They conform
fully with guidelines issued by WHO on
accepted field-based methods for the
microbiological analysis of drinking water.
The testing of water samples for coliform
bacteria uses a method called Membrane
Filtration.
In simple terms the process is as follows:
A known volume of sample water (100ml
or less for highly contaminated samples) is
filtered using a specific piece of apparatus
called the Membrane Filtration Unit (MFU).
Membrane Filtration Method
Water sample - filtered
through a membrane filter
MFU
Remove membrane
filter and place
on a nutrient
pad wetted with
sterile water
Incubation at 37/44ºC
INCUBATOR
Visual inspection
Introduction
Vacuum
on an absorbent pad
wetted with liquid
nutrient media
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