A biochemical test for separating paracolon groups.

The Arizona group of paracolon bacteria was first investigated by Peluffo et al. (1942). Studies on this group of organisms finally culminated in the report by Edwaards et al. (1947) that established an antigenic scheme of classification independent of the Salmonella scheme. The BethesdaBallerup group of paracolons was definitively studied by West and Edwards (1954), although the original Ballerup strain was described by Kauffmann and Moeller (1940), while the Bethesda strains were first reported by Edwards et al. (1948). Kauffmann (1954) has combined the Bethesda-Ballerup group with Escherichia freundii as the only difference between them was rapid fermentation of lactose by E. freundii, while in the Bethesda group lactose fermentation may be delayed 3 to 10 days and occasionally may not occur. Biochemically the Arizona and BethesdaBallerup groups are very closely related, the only constant difference being the liquefaction of gelatin by the Arizona group. This characteristic reaction may not occur with some strains of the Arizona group in less than 30 days. MIoeller (1954a) reported on the value of the Braun KCN test for differentiating this group, although 2 of 35 strains in the Arizona group departed from the usual behavior. The KCN test as described by Moeller is difficult to control, as results may vary with the size of the inoculum. MIoeller (1954b) also described methods for determining the distribution of the amino acid decarboxylases of the Enterobacteriaceae that were useful in classification. These tests required a special Danish peptone and close control for satisfactory evaluation of results. The need for a simple, reproducible method of determining decarboxylase activity useful in classification led to the present investigation.