The fourth international and (Dutch) national trial with reference materials for water microbiology

Abstract

A fourth trial with reference materials for water microbiology was organized. Forty-one Dutch laboratories and 37 laboratories of the EC participated. Each laboratory received four capsules of batches of reference materials with the test strains WR63 Enterococcus faecium and WR51 Staphylococcus warneri. Each capsule was reconstituted according to a standardized protocol and analysed by three different culturing methods: faecal streptococci by a reference method and by national standard methods (mf-techniques) and most probable number of faecal streptococci by national standard methods. The method of analysing the results was different from that in the three former trials. A method was used to exclude extreme observations in two steps. Next the repeatability (r) and reproducibility (R) were calculated. The calculated values of r and R were very low and those found for test strain WR63 almost impossible (theoretically) to improve. Differences found between methods could mostly be attributed to the medium used.<br>