A study of 186 strains belonging to eleven genera of the family Enterobacteriaceae and to three genera of the family Vibrionaceae has been carried out in order to determine their "versatility" towards 146 organic substrates tested as sole source of carbon and energy. Glucose was the only substrate used by all the strains; gluconate and glycerol were used by respectively 184 and 185 strains; 55 substrates were used by no one strains. The 90 substrates which were used by a fraction of the strains have served to establish a numerical classification of our strains, exclusively relied on these nutritional characters. In using the distinctness coefficient, it was possible to cut the dendrogram into 32 "classes" which may be clustered into 7 "groups" or 2 "sets": the obtained taxa are approximatively similar to the ones which are actually described on the basis of morphological and biochemical characters. The studied strains use 32.7 +/- 11.1 substrates on an average: the "eutrophic Klebsielleae group", which is the most versatile, uses 49.5 substrates on an average, and the "Shigella group", the lease versatile one, only uses 16.5 substrates on an average. The strains of the set 1 (100 strains) use 39.0 substrates on an average: all they belong to the family Enterobacteriaceae. The strains of the set 2 (86 strains) use 25.8 substrates on an average: they belong either to the family of Vibrionaceae, either to any little versatile genus of Enterobacteriaceae, namely Shigella, Proteus and Edwardsiella. The taxonomic inferences of this classification, exclusively established by means of the nutritional characters, are discussed.
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