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1 National Veterinary Institute, Oslo, -
2 Norwegian School of Veterinary Science, Oslo, -
3 Food and Feed Safety, National Veterinary Institute, Ullevaalsveien 68, Oslo, -, 0106, Norway
Existing methods for enumeration of viable Saprolegniaceae propagules in water are laborious, time consuming and prevent examination of large numbers of samples or samples with high spore loads. In the present study a microwell plate (MWP) assay for estimation of Saprolegniaceae in water samples, modified from Hagen (1992) was evaluated. The ability of the assay to recover Saprolegniaceae was assessed by applying it to spore suspensions with four different pre-determined concentrations, ranging from 500 to 10 000 spores per liter of samples tested. The method also was used to analyze a set of field samples and compared to a standard filtration method to ascertain its practicability. The MWP assay underestimated the number of spores in the test suspensions with pre-determined concentrations. The accuracy of the assay varied with spore concentration giving the lowest recovery (62.5%) at low spore numbers and the highest (86%) at intermediate concentrations (1000-5000 spores/L) for both isolates and growth media. The findings indicate that spores aggregate with increasing concentration. When applied to field samples the assay clearly distinguished between samples with presumptive differences in spore load, and yielded significantly higher counts than the filtration method. The results justify the MWP method for use in estimation of Saprolegniaceae in water bodies particularly relevant for monitoring of spore load in aquaculture as well as in ecological studies.
Key words: Saprolegniaceae, quantification method, spores, water
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