A study in test reproducibility between laboratories: Report of a Pseudomonas Working Party
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The results are reported of a collaborative study in laboratories of 17 tests commonly used for pseudomonads, together with statistical analysis of the results in the form of analyses of variance. The studies involved 59 strains.
The following tests showed good or reasonably good consistency between different laboratories: motility if checked by a Craigie tube, growth at 4 C, production of fluorescin, oxidation of glucose and sucrose, gluconate oxidation, hydrolysis of aesculin, arginine and casein, and gelatin hydrolysis by the tube method.
The following were less satisfactory: shape, size and arrangement of organismis, growth at 42 C, oxidase, acid from lactose, reduction of nitrate, acetic acid from ethanol, gelatin hydrolysis by the plate method, and the egg yolk reaction.
The following showed poor consistency or noticeable difficulties in performing or interpreting results of the test: growth at 37 C, the denitrification test of Stanier, Palleroni and Doudoroff, and hydrolysis of urea.
However, with several of the unsatisfactory tests the replicates within a laboratory showed much better reproducibility. This (together with other evidence on the importance of exact control of variables such as temperature, and time of reading, and the occurrence of mutants in some strains) suggests that careful attention to standardization may give much better testing methods. The considerable value of statistical analyses in such work is discussed.
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