Differentiation of Enterobacteriaceae and Vibrionaceae by a micromethod for determination of carbon substrate assimilation.

The assimilation techniques described for taxonomic study are unsuitable for routine diagnosis because of the need for purification and standardization of substrates, the great quantity of medium consumed and difficulties in interpreting the results. A standardized micromethod (API strip) for the study of carbon substrate assimilation by bacteria has recently been described (Zbl. Bakt. Hyg., I. Abt. Orig. A 255 (1983) 479-488). The prototype gallery used consisted of two strips of 32 microtubes each containing dehydrated carbon substrate. Each strip contained 30 tests plus positive and negative controls. The suspension medium was a synthetic semi-gel. A total of 914 strains of Gram negative rods representing 44 species of Enterobacteriaceae and Vibrionaceae were tested (Table 1). Automatic reading was performed after incubation at 32 degrees C for one day, or two days for slow growing bacteria using an ATB - 1500 reader (API System) linked to a HP 85 microcomputer (Hewlett-Packard). Most species showed typical carbon substrate assimilation patterns allowing their differentiation from other species within each genus (Table 2). The results obtained with the micromethod agreed in large measure with the nutritional patterns reported by other workers. It should be possible to use these results to construct a coherent framework of tests suitable for identifying species of Enterobacteriaceae and Vibrionaceae of clinical significance.