Acquisition of lactose-fermenting properties by salmonellae. I. Interrelationship between the fermentation of cellobiose and lactose.

The fermentation of lactose by salmonellae has seldom been accomplished, and in but few serological types (Kauffmann, 1954; Kristensen, 1948, 1955). In previous investigations we (Schafler and SchiLfler, 1959) succeeded in obtaining lactose-positive variants in 17 out of 30 salmonella strains belonging to different types, by means of 32 to 150 days of incubation on partially defined media containing lactose. All lactose-positive variants acquired the capacity of primarily fermenting cellobiose, which was fermented by the mutants of initial strains. At the same time, most variants acquired the capacity of fermenting salicin and arbutin. The other biochemical and antigenic properties of lactose-positive variants remained unchanged. We found similar connections between the acquired capacity of fermenting lactose and the fermentation of cellobiose, arbutin, and salicin in certain Escherichia freundii strains (Schaifler and Benes, 1959). It is the aim of the present paper to analyze the relationships existing between the fermentation of lactose and of cellobiose. An attempt was made to establish the mechanism by which the capacity to ferment lactose is acquired in salmonellae.