The Distinguishing Characteristics of Lactobacillus acidophilus

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Abstract
A collection of 103 lactobacilli was divided into 2 distinct groups on the basis of kind of acid formed, temp. reactions, colony type, carbohydrate fermentations, and inhibition by phenol and indol. Group (1) (58 cultures) agreed with the generally accepted concept of L. acidophilus and showed a high positive correlation in production of inactive lactic acid, formation of R or fuzzy colonies, failure to grow above 46[degree] or as low as 20[degree] C, fermentation of raffinose, and failure to ferment mannitol. As a rule these cultures formed more CO2, and a larger proportion of volatile acids, and grew in higher concentrations of phenol and indol than members of group (2). Cultures of group (2) produced inactive and dextro lactic acid and grew at 20[degree] or lower. The colony was usually of S or Y type or a mixture of Y and X, rarely of the pure X type. Mannitol and salicin were nearly always fermented; raffinose, only occasionally. These strains were less active than cultures of group (1) in formation of volatile acids and COa, and were inhibited by relatively dilute solutions of phenol and indol. Group (3) (15 cultures) differed from (1) in growing at 20[degree]. There was also sufficient variation in other characters to warrant setting them aside, at least as atypical cultures. All cultures produced some volatile acids[long dash]a mixture of formic, acetic and butyric. A large proportion of those of known intestinal origin were in the acidophilus group; a few of the dental cultures were also of this type, but the greater part belonged in the group producing inactive plus dextro lactic acid.