Fermentation Studies on Lactobacillus Acidophilus and Lactobacillus Bulgaricus

Abstract

Since it is now a commonly accepted fact that strains of Lactobacillus acidophilus are implantable in the human intestinal tract and are of some therapeutic value whereas strains of Lactobacillus bulgaricus are not implantable and hence are of little or no therapeutic value, it is extremely important to have a reliable method for the differentiation of the two species. Obviously, proof of implantability would serve as the final criterion of a culture of Lactobacillus acidophilus, but as the carrying out of extensive implantation experiments is a laborious procedure, a number of presumptive methods have been proposed. A survey of recent literature shows that the final differentiation is frequently made by a study of the abilty of the organism to produce acid from maltose, sucrose and levulose, those strains that produce acid from the three sugars being considered L. acidophilus, and those strains that do not ferment these sugars, L. bulgaricus. The fermentation of maltose, levulose and sucrose by L. acidophilus has been generally agreed on. On the other hand, while L. bulgaricus was originally described by Grigoroff 1 as fermenting these three sugars, Rahe2 differentiated it from other acid-resisting organisms by its inability to ferment maltose. He found that some strains fermented sucrose and levulose. Kulp and Rettger3 and Kulp4 in extensive studies of L. acidophilus and L. bulgaricus were unable to secure any culture of typical L. bulgaricus that would ferment maltose, sucrose or levulose. They recognized the existence, however, of borderline strains that fermented maltose.