Response of bifidobacterium species to growth promoters in human and cow milk.

We used an in vitro assay to study and compare the growth-promotional activity of protein and nonprotein components in human milk (HM) and cow milk (CM) samples for infant strains of Bifidobacterium species. HM samples varied considerably in growth-promotion activity for Bifidobacterium bifidum var pennsylvanicus, Bifidobacterium infantis, and Bifidobacterium breve. Pooled CM samples showed similar but less variable levels of activity when compared with HM samples. Separation of milk samples by ultrafiltration into protein nitrogen and nonprotein nitrogen (NPN) fractions revealed that the bifidobacteria growth-promotion activity of HM was associated primarily with the NPN fraction, whereas activity in CM whey was found in both protein nitrogen and NPN fractions. Testing of purified CM whey proteins showed that alpha-lactalbumin and lactoferrin were potent growth promoters, showing greater activity for B. infantis and B. breve than for two strains of B. bifidum. Conversely, N-acetylglucosamine and purified gastric mucin were highly active for B. bifidum strains but inactive for other Bifidobacterium species. Collectively, the data indicate that both protein nitrogen and NPN factors in HM and CM promote the growth of bifidobacteria and suggest that Bifidobacterium species differ in responsiveness to protein and oligosaccharide growth promoters.