Bacterial Variations in Salicin Medium

Abstract

Most investigators have concerned themselves with the variation in morphological and colonial characteristics, especially in regard to the smooth (S) and rough (R) types. Neisser, 1 in his first work on variation, noted that a nonlactose-fermenting, colonlike organism gave daughter colonies which fermented lactose. Burri 2 observed this same phenomenon in regard to sucrose fermentation, when he studied an organism isolated from fermenting grass.

Many investigators have found no characteristic biochemical difference among their variants when the original culture was grown in media containing carbohydrates or higher alcohols except lactose.

Variation occurs spontaneously under ordinary conditions of cultivation, and also with environmental stimuli such as the presence of sugars, dyes, or changes in temperature. The presence of salicin in the medium as the environmental stimulus was chosen in this present investigation. The chief object was to study the characteristics of the variants which were produced when separate individual colonies from the mother culture were successively transplanted in salicin broth for 15 times.

A group of 36 salicin-negative organisms were selected, 31 of these belonging to the Escherichia genus and 5 to the Aerobacter genus. Eosin-methylene blue plates were streaked from these cultures, and 10 colonies which showed no gas production in salicin medium were transferred every third day to fresh tubes of salicin medium for at least 15 times. The percentages of gas produced were recorded after 7 days incubation at 37°C. As an example, a record of the acquired ability of culture E. anindolica G. to ferment salicin is shown in Table I.

Of the 36 organisms used, 22 (220 sub-cultures) remained negative to salicin through-out the 15 transplants in salicin broth. Of the other 14 organisms (140 sub-cultures), there were from 1 to 10 of the sub-culturesof each organism which acquired the ability to ferment salicin after from 1 to 12 transplants.