Dissociation and Filtration of Lactobacillus Acidophilus

Variants in the dissociation of Lactobacillus acidophilus have been observed by numerous investigators. One aspect of this phenomenon, however, merits particular attention. In other bacterial species one may follow transitional forms from rough (R) to smooth (S) and vice versa. With L. acidophilus of intestinal origin, on the contrary, variations from R to S are a matter of common observation, but variations from S to R are exceptional. Hadley, Bunting and Delves 1 reported success in obtaining rough variants by marginal dissociation of dental strains, but no mention is made of any similar experience with intestinal strains. In a previous communication 2 attempts to force the dissociation from S to R were described, and the conclusion was reached that it was exceedingly difficult to obtain antigenically pure R forms from S. Since thus far attempts to produce a stable R variant from a S strain had consistently failed it seemed worth while to continue efforts by means of methods commonly employed in the dissociation of' other bacterial species. The present investigation is concerned with the action of bacteriophage on L. acidophilus cultures, serial transfers in lithium chloride broth and repeated marginal fishings from old colonies. It is almost impossible to establish rigid criteria for R and S forms, yet some definition is necessary in order to clear the way for the interpretation of results. The colonial characteristics most commonly associated with S forms as described by Hadley are: smooth, regular, convex,,, while R forms are : rough, irregular, flat. However, many strains of L. acidophilus fall between these two extremes. In general it may be said that the typical R strain of L. acidophilus of intestinal origin used for therapeutic purposes is distinctly filamentous or fuzzy in appearance on solid mediums. Unless distinct radiating threads of unequal lengths are visible to the naked eye in colonies grown for from three to seven days on casein digest agar they are not designated as R in this report. These threads are more striking in deep than in surface colonies. A smooth colony is round or elliptic with an entire margin. Usually R colonies are diffuse, flat, dull and gray as compared with