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By harnessing
the power of fluorescent cell labelling and ultra-sensitive laser
scanning, four critical drinking water quality tests can now be
rapidly performed on just one instrument. Using the ChemScan®
RDI, from Chemunex, it is now possible to substantially reduce
the operator time required to complete analysis of water samples
for the detection of Cryptosporidium and Giardia
and to obtain results for Escherichia coli and coliforms
in less than four hours, with sensitivity down to a single cell.
This speed
to result considerably cuts the time currently required to conduct
such tests, and the introduction of automation reduces operator
fatigue. In combination, these benefits provide the drinking water
industry with a unique opportunity to both enhance consumer protection,
through near real-time, fatigue-free testing for potential pathogens,
and to realise previously unavailable operational savings.
Detecting
Cryptosporidium and Giardia
Following concentration and purification of water samples using
existing techniques, captured Cryptosporidium and Giardia
are fixed on slides and labelled using fluorescently conjugated
antibodies. Individual cells are then automatically detected and
counted within three minutes using ChemScan RDI's advanced
laser scanning technology. This has the capability to accurately
differentiate labelled oocysts and cysts from background fluorescence.
Results are
displayed as direct cell counts indicating the number of cysts
or oocysts present. A scan map, showing the location of every
labelled cell on the filter is also produced. When suspected oocysts
or cysts have been detected, their presence on the filter can
be confirmed, if required, using an epifluorescence or DIC microscope
fitted with an automatic stage driven by the ChemScan RDI.
Samples can also be stored for re-analysis, should the need arise,
and all the data is completely secure.
Current manual
microscope based methods for detecting labelled protozoa on slides
are slow, typically taking 20-120 minutes per slide, and require
highly trained operators, who must work on strictly limited shifts
to minimise fatigue. The ChemScan RDI provides the capability
to automate the analysis, minimise operator fatigue and substantially
increasing the throughput. At 12-15 slides per hour, this is 6-7
fold higher than is achievable with current manual methods, yet
the system accuracy and sensitivity has been shown to be at least
as good as manual microscopy-based methods.
Detecting
E.coli and coliforms
The detection and counting of Escherichia coli and coliforms
with the ChemScan RDI is based on the use of fluorescently
labelled substrates aimed at specific enzymes induced during sample
preparation. In the case of E.coli, b-glucuronidase
is the target, while for coliforms it is b-galactosidase.
Total test time including labelling and laser scanning is less
than four hours, with sensitivity down to single cells. Current
'rapid' methods for the detection of E. coli and coliforms
still require 18-24 hours to produce a result, and are not quantitative.
This is a significant limitation in those circumstances where
results are needed fast, such as for emergency testing. A further
benefit of analysis on the ChemScan RDI is that, unlike
PCR based methods, it clearly differentiates live and dead cells.
The availability
of near real-time results for these key indicator organisms provides
water utilities with substantial support in their continuing efforts
to improve consumer protection and streamline operations. Speed
to result is particularly valuable in situations such as monitoring
of purification works, random testing of consumer outlets (usually
on sites that are likely to pose, or have already posed, problems
in the past, e.g. dead-ends etc.) and review of water quality
in situations where quality may have been compromised such as
after heavy rain, pipe bursts, engineering work etc.
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