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One of the
world's major water utilities, Anjou Recherche, Vivendi Water,
has successfully completed trials of the automated ChemScan RDI
system, from Chemunex, for the enumeration of Giardia and
Cryptosporidium in water supplies. The Company found that
ChemScan RDI provided a more sensitive, reliable and
quicker method for the detection of these micro-organisms, compared
with the previous manual method.
Following its successful evaluation, the ChemScan RDI has been installed as the main system for analysis of Giardia and Cryptosporidium in the routine laboratory at Anjou Recherche, Vivendi Water. This will enable the Company to provide a more efficient monitoring service for the presence of these pathogenic organisms in water supplies.
Prior to the study, Anjou Recherche, Vivendi Water, followed the traditional method of analysing Giardia and Cryptosporidium in water, which included a manual detection step of the stained organism by direct epifluorescence microscopy. However, as manual inspection was time consuming and prone to errors in observation, the Company evaluated the ChemScan RDI system with the aim of improving the final enumeration step.
Anjou Recherche, Vivendi Water's initial investigation on ChemScan RDI using surface waters, showed that the system was capable of detecting equivalent or higher numbers of Cryptosporidium oocysts, compared with direct microscopic observation. This was achieved with a four to six times decrease in the analysis time. Similar results were found when the ChemScan RDI was used to analyse water samples for Giardia.
The introduction of ChemScan RDI will enable Anjou Recherche, Vivendi Water to improve its overall monitoring service for Cryptosporidium and Giardia. The new standardised method for labelling and detecting these organisms produces results that are more consistent and reliable than traditional methods. Also, the reduction in the analysis time will allow a higher sample throughput in the testing laboratory. ChemScan RDI will subsequently enable Anjou Recherche, Vivendi Water to provide a more rapid response to the occurrence of Cryptosporidia and Giardia contamination in water supplies.
Detection of Giardia and Cryptosporidium using the ChemScan RDI is based
on a standardised method developed within the water industry, where cysts and oocysts are stained using a highly sensitive dapi/ fluorescent monoclonal antibody combination.
Giardia and Cryptosporidium are first concentrated and purified from water samples using existing techniques; the organisms are then captured on the surface of a membrane filter and labelled with specific antibodies against each organism. By combining one antibody directed against the cyst wall of Giardia, together with one targeted against the Cryptosporidium oocyst, the labelling is highly specific and enables both organisms to be detected simultaneously. Individual cells are then automatically detected and counted using ChemScan RDI's advanced laser scanning technology. This has the capability to accurately differentiate labelled oocysts and cysts from background fluorescence.
It takes less than three minutes for ChemScan RDI to scan the entire sample. Results are then displayed as direct cell counts indicating the number of cysts or oocysts present, together with a scan map showing the location of every labelled cell on the filter. When suspected oocysts or cysts have been detected, their presence on the filter can be confirmed, if required, using an epifluorescence microscope or DIC (Differential Interference Contrast) microscope fitted with an automated stage driven by the ChemScan RDI. By clicking on any point on the scan map, the automated stage positions that micro-organism in the centre of the microscope field of view for visual confirmation. Complete analysis of a sample takes around five minutes, compared with 20-120 minutes per slide by the manual method.
Cryptosporidium and Giardia have caused a number of contamination scares over recent years. These water-borne parasites cause diarrhoea, nausea and vomiting, and are a major public health concern since they can lead to death among individuals with depressed immune systems, children or the elderly.
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