Bifidus factor. I. A variant of Lactobacillus bifidus requiring a special growth factor

Human milk contains an essential growth factor for a variant of Lactobacillus bifidus. In contrast cow's milk exhibits only very low activity for this variant. The variant has been named L. bifidus var. Penn. The bifidus factor in human milk is not destroyed or altered in its activity by autoclaving. The ash is inactive. A large number of organic compounds, including microbiological growth factors, yeast extract, and vitamins not represented in the original medium, as well as carbohydrates and several vegetable extracts, have been tested for growth-promoting activity and have been found ineffective. Very slight activity was exhibited by liver compounds. Morphologically, L. bifidus var. Penn is identical with regular strains of L. bifidus. Serologically, it differs from the regular strains tested. It tends to mutate and then loses its requirements for human milk. Attempts to adapt a regular strain of L. bifidus to human milk were unsuccessful. L. bifidus var. Penn may become mucoid without loss of its dependence on human milk. For L. bifidus var. Penn maltose cannot replace lactose as source of carbohydrate. Except in its requirement for lactose and for the special growth factor, differences in the metabolic pattern of L. bifidus var. Penn from the regular bifid strains have not been found.