Lactobacillus bifidus

Abstract

L. bifidus appears in the feces of breast-fed infants 3-4 days after birth, and predominates as long as breast milk is the sole diet. It is isolated easily by the acid-broth selective method, but, though a facultative anaerobe, requires strictly anaerobic conditions in primary isolation. In its morphology and most of its cultural characteristics it resembles L. acidophilus; both reveal branching under certain special conditions. Its antigenic properties are not well defined, but they exhibit, in general, a serological resemblance to L. acidophilus. L. bifidus possesses the same tolerance for acids, alkalies, indol, phenol, crystal violet, basic fuehsin and lysozyme as does L. acidophilus. Both produce lactic acid as the chief product, the bulk of which is inactive. While there are slight differences between L. bifidus and L. acidophilus, they can be accounted for by normal variation within the sp. or type. The authors believe that L. bifidus should be regarded as a variant of the sp. in which L. acidophilus is the central type.