The distinguishing characteristics of Lactobacillus acidophilus

It requires only a casual examination of the literature to show that there is much confusion in regard to the differentiation of the members of the lactobacillus group. While bacteriologists who have worked with this group may have quite definite con-cepts of the various species it is difficult to translate those con-cepts into concrete terms which define a biological species. This is especially true of the acidophilus cultures, since they have been selected more on the basis of their ability to grow under certain prescribed conditions than because of compliance with taxonomic criteria. Much of the confusion in bacteriological nomenclature is due to the use of a limited number of cultures in determining a basis for describing species and to reliance on characters which are incon-stant and have little taxonomic significance. The natural group-ing of bacteria is based on fundamental physiological characters which the members of these groups possess in common. Corre-lated with these are more superficial, and sometimes more obvious, characters which may permit an easy identification. In establish-ing a classification it is clear that the emphasis should be placed more on the stable basic characters and less on those which are superficial. The isolation of cultures for identification is more or less a matter of chance and, if only a few are studied, there is always a possibility that these are not representative of the species as it occurs in nature. We have used as many cultures as the laborious nature of many of the determinations would permit