Optimization of the Envirochek capsule method and immunomagnetic separation procedure for the detection of low levels of Cryptosporidium in large drinking water samples

The method for concentration of Cryptosporidium oocysts in large drinking w ater samples using the Envirocheck capsule has been optimized for the detec tion of low levels of oocysts. Elution from the filter by contact time and vortex agitation gave 68% oocyst recovery. Centrifugation (1,250 g; 30 min; 4 degrees C) improved recovery to 94% without morphological damage of the oocysts. Increasing the ratio of magnetic beads to sample volume in the IMS procedure led to 69% efficiency. In these conditions, the overall recovery of the procedure was 49% as assessed with low oocysts spike doses in 100 l itres tap water samples. The methodology described allows the detection of 0.1 oocyst per litre when 100 litres samples are processed.