Het vijfde internationale en (nederlandse) nationale ringonderzoek met referentiematerialen voor watermicrobiologie

Thirty-nine Dutch laboratories and 33 laboratories of the EC participated in a fifth trial with reference materials for water microbiology. Reference materials with the test strains WR63 Enterococcus faecium and WR52 Staphylococcus warneri were used. The materials were analysed for total aerobic viable bacteria by a reference method and the national standard method, both with incubation at 22 and 37 degrees C. After statistically analysing the results, the repeatability (r) and reproducibility (R) were calculated. Very good results were found for r and R. Especially the values of r found with the material with strain WR63 were very close to the theoretical optimum.EG/BCRHIMHVH

Certificatie van Salmonella in melkpoeder, een voorstudie

Abstract niet beschikbaarA feasibility study was undertaken for the certification of a reference material containing low numbers of Salmonella. A batch of 8800 capcules was prepared and eleven laboratories each enumerated 50 capsules from this batch, according to a standardized procedure. The results from four laboratories were excluded from the analysis of data after the first step of the statistical analysis based on their results found for homogeneity and mean contamination level. The remaining seven laboratories found contamination levels that did not differ significantly from each other. The mean contamination level found by these seven laboratories was 5.65 cfu/capsule. The homogeneity, based on all counts by these seven laboratories, was not fully conform to a Poisson distribution. A ratio of variance to mean of 1.18 was found, which is considered acceptable. The proportion of negative capsules found in the study was 0.58% and the upper limit of the corresponding confidence interval (one sided, (alpha = 0.05) was 1.8%. Concluded was that the batch prepared is of sufficient to be used for a certification study.EG/BCR HIGB VH

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

A third trial with reference materials for water microbiology was organized. Thirty-eight Dutch laboratories and 39 laboratories of the EC participated. The design of the trial was the same as in the first and the second trial. Also the test strains were the same: WR1 Escherichia coli and WR3 Enterobacter cloacae. The reference materials of the third trial were more stble and homogeneous than the batches used in the first and the second trial. Improved materials and protocols resulted in better performance in participating laboratories. The variation between the results was less than in the first and the second trial. Insufficient inhibition of the growth of test strain WR3 at a nominal temperature of 44 C, in some laboratories, showed that incubation at 44 C still need some improvements. The use of reference materials may therefore be very useful.<br

Het vierde internationale en (nederlandse) nationale ringonderzoek met referentiematieralen voor de watermicrobiologie

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.EG/BCRHIMHVH

[Bepaling van het aantal Bacillus cereus en Staphylococcus aureus kiemen in referentie materialen voor de levensmiddelenmicrobiologie. BCR Food/trial 5.]

Abstract niet beschikbaarA collaborative study was organised to test the newly developed reference materials (RM's) for Bacillus cereus and Staphylococcus aureus. Fourty one laboratories participated in this international collaborative study, each laboratory testing 5 capsules for each of the 2 types of RM. Each series of capsules contained an uncontaminated sample. For use each capsule had to be reconstituted according to a standardized procudure. Both types of RM were enumerated on one non-selective and three selective agars (one of which was chosen by the participating laboratory). The values found for repeatability (r) and reproducibility (R) were ca 1.4 and ca 1.8 respectively independent of the type of medium used. The stability of the RM's was extremely good due to the use of spores in this material. The r and R values were higher for S. aureus than for B. cereus. The r value was 1.6 and the R value, depending on the type of medium used, ranged from 2.0 to 3.4. The stability of this material was poor when stored at 22 degrees C but at -20 degrees C no decrease in contamination level was observed over 70 days of storage.EG/BCRRIV

Het derde internationale en (nederlandse) national ringonderzoek met refentiematerialen voor de watermicrobiologie

A third trial with reference materials for water microbiology was organized. Thirty-eight Dutch laboratories and 39 laboratories of the EC participated. The design of the trial was the same as in the first and the second trial. Also the test strains were the same: WR1 Escherichia coli and WR3 Enterobacter cloacae. The reference materials of the third trial were more stble and homogeneous than the batches used in the first and the second trial. Improved materials and protocols resulted in better performance in participating laboratories. The variation between the results was less than in the first and the second trial. Insufficient inhibition of the growth of test strain WR3 at a nominal temperature of 44 C, in some laboratories, showed that incubation at 44 C still need some improvements. The use of reference materials may therefore be very useful.EG/BCRVHIHIM

Detectie van Listeria monocytogenes in de aanwezigheid van competatieve micro-organismen met gebruik van referentiematerialen, BCR-Food Trial 4

Abstract niet beschikbaarA trial with 42 laboratories participating, was organized in May 1990 to test the L.monocytogenes reference materials in combination with reference materials containing competitive microorganisms. The materials were tested by 2 methods, one standardized for all laboratories (SM method) and the other method chosen by the laboratories themselves (OWN method). Thirty samples were tested by each method of which nine were negative for Listeria. The contamination level of the L.monocytogenes capsules was 4.9 cfu/capsule. Each laboratory was expected to find the organism in 18 or more out of the 21 L.monocytogens contaminated samples. The total contamination of microorganisms was 2.9 x 10-4 cfu/capsule. Using the standard method Listeria monocytogenes was detected in 79.3% of the contaminated samples, and 45% of the participating laboratories made the expected number of isolations. With the OWN method these percentages were 78.1% and 52.5% respectively. Concluded was that the materials tested are suitable to test the performance of the detection method for Listeria in a laboratory.EG/BCR VHI HIG

Telling van Salmonella in referentie monsters, een ringonderzoek met twaalf laboratoria

De telling van Salmonella in referentiemonsters volgens een methode ontwikkeld door het RIVM werd getest door 12 europese laboratoria. De methode bestaat uit drie stappen: - oplossen van de capsule in physiologische zoutoplossing - herstel van sublethaal beschadigde cellen in Plate Count Agar - selectieve groei in Violet Rood Gal Glucose Agar. Elk laboratorium ontving 50 Salmonella referentiemonsters tesamen met een gedetailleerde beschrijving van de methode. Analyse van de data met behulp van Gegeneraliseerde Lineaire Regressie gaf aan dat na het weglaten van de resultaten van een laboratorium er geen verschil in het besmettingsniveau tussen de laboratoria kon worden aangetoond. Drie laboratoria vonden een significant grotere variatie in het aantal kiemen tussen de capsules dan verwacht kon worden volgens een Poisson verdeling. Alle kolonies die werden bevestigd bleken Salmonella te zijn. Geconcludeerd werd dat deze ontwikkelde quantitatieve methode geschikt is voor de certificering van deze referentiemonster.Abstract not availableEG/BCR VHI HI

Detectie van Salmonella in de aanwezigheid van begeleidingsflora met behulp van referentiemonsters. BCR-FOOD Trial 2.

Abstract niet beschikbaarThe detection of Salmonella in the presence of competitive microorganisms was tested with the use of reference samples. Thirtyeight laboratories investigated 25 samples of which 5 were negative for salmonella. The Rappaport-Vassiliadis broth was used as reference (RV- method) and compared with a selective enrichment broth chosen by the laboratory itself (OWN-method). The Salmonella samples had a contamination level of 5.48 salmonellae/capsule, the competitive microorganisms of about 2x10 cfu/capsule. The strains used for competitors were: Enterobacter cloacae, Escherichia coli, Pseudomonas aeruginosa and Proteus mirabilis. Significant differences were found between laboratories and between the RV and OWN method. With the RV method 42% of the labs found 19 or 20 positive isolations ; the percentage positive isolations (averaged over all labs) was 81.5%. With the OWN method only 19% of the labs found 19 or 20 positives, the percentage positive isolations was 62.3%. Eight laboratories found one or more of the Salmonella negative samples positive for Salmonella. The competitive microorganisms reference samples is mutable to test the isolation procedure for Salmonella under more realistic circumstances.EG/BCR VHI HIG

Stabiliteit en homogeniteit van microbiologisch referentiemateriaal: enkele statistische modellen

Microbiological reference materials are being developed by the RIVM since several years. These materials consist of capsules filled with milkpowder artificially contaminated with a bacteria test strain of choice (i.e. Escherichia coli, Enterobacter cloacae, Salmonella typhimurium). Both from longterm stability tests, and from short-term challenge tests at different storage temperatures, it is clear that these materials cannot survive forever. Standard statistical techniques for quality control, assuming both a stable process and the Normal distribution cannot be used. In this report we will deal with these non-standard problems.EG/BCRHIMHVH