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 anaerobic bacteria of the genus Bifidobacterium in vitro. The present study was designed 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 the 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 contrast, human Lf (huLf) from mature milk promoted the growth of B. bifidum and was inactive for B. infantis and B. breve, while bLf from colostrum was devoid of bifidobacteria growth promotion activity. Changes in the iron content of Lf did not alter the bifidobacteria growth promotion activity of either bLf or huLf preparations. Competitive binding studies with biotinylated milk bLf showed that binding of bLf was inhibited by unlabelled bLf and huLf but not by beta-lactoglobulin, alpha-lactalbumin or transferrin, Binding of bLf to B. bifidum and B. breve was c. 40-fold higher than binding to Escherichia 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 Bifidobacterium spp. in vitro is independent of the iron saturation level for Lf and suggest that binding of Lf to bifidobacteria cells may be involved but is not sufficient for stimulation of bifidobacterial growth.