A specific mutant of L. bifidus (var. Penn) isolated from the feces of a breast-fed infant has shown no growth in the usual medium satisfactory for most strains of L. bifidus. It required for its propagation the addition of a specific "growth factor" present in human milk. Cow's milk had only 1/30 to 1/100 of the activity of human milk. The average relative activity was highest for the human colostrum, closely followed by rat colostrum, then by human milk, rat milk and cow's colostrum (taken on the first day). All the other milks tested, in particular the milk from ruminants such as sheep and goats in addition to cow's milk, have shown only very low activity. Sow's and mare's milk are slightly more active, guinea pig milk is inactive. This microbiologic growth factor is different from all known vitamins and growth factors. Very slight activity was exhibited by liver compounds, and practically none by yeast or meat. Meconium is highly active. Human semen, uterine (cervical) mucus, gastric juice (even in a case of pernicious anemia), saliva, amniotic fluid, and tears are also very active. The growth factor occurs in low and higher molecular form in human milk. In meconium it is present in undialyzable form. Purified blood group substance A and B are highly active. From human milk levorotatory active products were obtained containing N-acetyl glucosamine, fucose and galactose, but no amino acids. N-acetyl glucosamine and N-acetyl galactosamine were only slightly active.
L. bifiidus var. Penn contains a specific enzyme which inactivates the microbiologic growth factor required by the same strain. The enzymatic inactivation of meconium or purified blood group substance as growth factor is accompanied by the reduction of its serologic titer as specific blood group and by the liberation of dialyzable reducing substances, chiefly acetyl-glucosamine.
- Received June 3, 1952.
- Copyright © 1953 by the American Academy of Pediatrics