The general problems of probabilistic identification of bacteria are discussed, particularly choice of taxa, choice of tests, assignation of probabilities and variation with geographical distribution, method of modification of probabilities as information is obtained, identification levels and linkage of tests.A study is described of the probabilistic identification of 1079 reference strains, and 516 field strains of Gram-negative, aerobic, rod-shaped bacteria. The field strains were identified both on the test results obtained by sending laboratories and test results in our laboratory. Identification rates for fermentative bacteria of 90.8 % for reference strains and 89.4 % for field strains were obtained, and for non-fermentative bacteria of 82.1 % and 70.8 % respectively. The field strains were received because they were difficult to identify in the medical diagnostic laboratory; higher rates of identification might be expected for typical strains.
SUMMARYThe methods incorporated in the computer program used in a trial of computeraided identification of bacteria are described. The identification method is based on Bayes's theorem and allows for dependent tests and missing data in the probability matrix. It was found useful in developing the method to take account of the occurrence of errors in bacteriological testing. The method suggests a definite identification only if the Bayesian probability of one of the taxa exceeds a threshold level; if not, a separate procedure selects the best tests to continue the identification.
SUMMARYA numerical classification study was carried out on I 77 strains of Klebsiella and related groups. Three methods of numerical classification were used : median sorting, single linkage cluster analysis and minimum spanning tree. All three contributed to the final decision on the taxa, but yielded substantially the same results. Of the three, the median sorting, if used alone, would have provided the most information.The validity of the genus Klebsiella was confirmed but the inclusion of the three recognized species of Enterobacter in one genus was not confirmed. The genus Klebsiella was divided into six taxa, one of which is proposed as K. mobilis synon. Enterobacter aerogenes. E. cloacae occupied a rank similar to that of the genus Klebsiella, while E. liquefaciens was most closely related to the genus Serratia and it is proposed to include it as S. liquefaciens. Enterobacter 'pigment&' was found to be closely related to Chromobacterium typhiyavum.
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