Dissociation and Lactase Activity in Slow Lactose-Fermenting Bacteria of Intestinal Origin.

In 1918 Bronfenbrenner and Davis observed that intestinal bacteria were frequently encountered which failed to show up as lactose fermenters in the routine diagnostic procedure, but which readily did so on subsequent cultivation in media containing lactose in higher concentrations. Studies of the conditions under which the fermentation of lactose by these organisms could be enhanced, with the purpose in view of improving methods for their detection, were reported at that time. Bacteria exhibiting similar variability in fermentation were early described by Neisser (1906) and Massini (1907), under the name Bacillus coli-mutabile. They have been studied more recently by Kriebel (1934), Sandiford (1935), and, with special reference to bacterial variation, by Lewis (1934) and Hall (1935). In the course of continued studies of the metabolism of slow lactose-fermenting bacteria of the Escherichia coli type, we have made some observations which we believe may contribute toward elucidation of metabolic mechanisms which determine lactose fermentation by these organisms. The cultures used in the present study were isolated from unselected human fecal specimens by plating on lactose agar containing China blue-Rosolic Acid (C.R.) indicator (Bronfenbrenner, 1918). Of six samples examined, slow lactose-fermenting organisms were obtained from one, in which they were the predominating type. Several single colony strains of both the slow-fermenting and typical E. coli varieties were transferred