Ability of lactoferrin to promote the growth of Bifidobacterium spp. in vitro is independent of receptor binding capacity and iron saturation level

Lactoferrin (Lf) is an iron-binding protein which has been shown to inhibit the growth of various bacterial pathogens and promote the growth of anaero bic bacteria of the genus Bifidobacterium in vitro. The present study was d esigned to investigate whether the bifidobacteria growth promotion activity of Lf is correlated with either the binding of Lf to bifidobacterial cells or the iron saturation of Lf. Bovine Lf (bLf) from mature milk increased t he growth of B. infantis and B. breve in vitro in a dose-dependent fashion, while much less growth promotion activity was found for B. bifidum. In con trast, human Lf (huLf) from mature milk promoted the growth of B. bifidum a nd was inactive for B. infantis and B. breve, while bLf from colostrum was devoid of bifidobacteria growth promotion activity. Changes in the iron con tent of Lf did not alter the bifidobacteria growth promotion activity of ei ther bLf or huLf preparations. Competitive binding studies with biotinylate d milk bLf showed that binding of bLf was inhibited by unlabelled bLf and h uLf but not by beta-lactoglobulin, alpha-lactalbumin or transferrin, Bindin g of bLf to B. bifidum and B. breve was c. 40-fold higher than binding to E scherichia coli, Colostrum bLf was also found to bind to B. bifidum and B. breve, despite a lack of in-vitro growth promotion activity: Collectively, these results demonstrate that the ability of Lf to promote the growth of B ifidobacterium spp. in vitro is independent of the iron saturation level fo r Lf and suggest that binding of Lf to bifidobacteria cells may be involved but is not sufficient for stimulation of bifidobacterial growth.