A Study Of Bacillus Bulgaricus: (Synonyms Bacillus of Massol, B. acidophilus, Boas-Oppler bacillus, Bacillus panis fermentati, Streptobacillus lebenis, Leptothrix buccalis.)

Abstract

In a preliminary note, presented at the meeting of The Society of American Bacteriologists at Baltimore, 1908, we reported the finding of a bacillus resembling B. bulgaricus, an organism which has been studied extensively because of the fact that Metchnikoff recommends its use in the artificial preparation of buttermilk. According to our investigations, this bacillus is the principal agent which produces lactic acid in salt-rising bread, the acid thus formed decomposing sodium bicarbonate, with the liberation of carbon dioxide. Salt-rising bread, as is well known, is started by a mixture of meal, usually cornmeal, with milk, saleratus, and a small amount of salt. The liberation of carbon dioxide causes the rising of the dough. We ascertained that the active bacillus was present in the cornmeal, since a mixture of cornmeal and sterilized milk revealed the organism in large numbers and practically in pure culture. This bacillus is somewhat difficult to cultivate, and we found that the ordinary laboratory media are quite inadequate. Sterilized milk or media prepared from milk seem the most favorable, although the addition of glucose to broth increases multiplication if the incubation temperature is high enough, i. e., 370 C. or higher. Several descriptions of bacilli producing a large amount of acid, much more than the ordinary lactic-acid bacteria, have appeared in the literature, and the suggestion of Metchnikoff has induced several workers to take up the study again. Fermented milk beverages, especially, have been investigated, and organisms found which resemble each other closely. They are described as large bacilli, which occur singly or in filaments, produce large amounts of acid in milk (up to three per cent), and are gram positive. The descriptions are not complete, owing probably to the fact that the organisms do not