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).
7
2
Introduction
Membrane Filtration Method
Water sample - filtered
through a membrane filter
INCUBATOR
MFU
Vacuum
Remove membrane
filter and place
Visual inspection
Incubation at 37/44ºC
on an absorbent pad
wetted with liquid
nutrient media
on a nutrient
pad wetted with
sterile water
To Next Page
Loading...
Need help?
General
