Flow
cytometry (FCM) studies have been used for the quantification of microbial
cells in drinking water. A recent study has shown that drinking water contains100
to 10,000 times more living cells than the conventional plate count method
would suggest.
The
microbial content of water is normally assessed using the heterotrophic plate
count (HPC). The HPC method involves growing any bacteria present in a sample
of water onto solid nutrient media (incubated at a warm temperature), and the
colonies formed are then counted.
The
weakness with the HPC method are the incubation time and the fact that only a
fraction of the living cells actually present in samples are counted (the
so-termed ‘viable but non-culturable’ microorganisms).
The
utilisation of FCM methodology can be used to determine, more accurately, the
total cell count in a water sample within a matter of minutes.
FCM
works by staining any cells contained in a sample with fluorescent dyes, which
bind to DNA. The cells are then passed in single file through a glass
capillary, where they are exposed to a beam of light from a laser. The
resultant scatter and fluorescence signals are picked up by detectors, and
analytical software is used to classify each individual particle (cell).
Posted by Tim Sandle
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