In vitro and in vivo (LD50) effects of human lactoferrin on bacteria.

The in vitro and in vivo effects of human lactoferrin (LF), apoLF, iron saturated LF and of different iron containing compounds (ferric chloride, ferric sodium citrate) were studied on Escherichia coli, Salmonella typhi-murium and Pseudomonas aeruginosa reference and wild-type strains with well-defined virulence markers (i.e. enterochelin, aerobactin production). LF exert in vitro antibacterial effect, and iron-free Vogel-Bonner medium proved to be suitable for its determination. The effect of intraperitoneally administered LF could not be evaluated because of its aspecificity, as any treatment (e.g. saline, Ringer solution) before bacterial challenge activated macrophages. In contrast to the in vitro results, intramuscular challenge failed to inhibit bacterial growth in vivo, as siderophores produced by bacteria were able to acquire lactoferrin-bound iron. LF treatment, like iron addition, enhanced the virulence of bacteria in mice, whereas apoLF - using iron present in the body fluids - turned to LF being unable to acquire siderophore-bound iron from bacteria. These findings do not support the literary view that LF would be useful as an antimicrobial drug.