Evaluation of the antimicrobial effect of lactoferrin on Porphyromonas gingivalis, Prevotella intermedia and Prevotella nigrescens.

The antimicrobial effect of lactoferrin (apoLf) on the oral, black-pigmented anaerobes Porphyromonas gingivalis, Prevotella intermedia and P. nitrescens has been studied. ApoLf did not kill any of these species but it did inhibit the growth of P. gingivalis, while iron-saturated Lf (FeLf) had no effect. The other two species were unaffected by apoLf. This growth inhibitory effect of apoLf could not be explained on the basis of chelation of inorganic iron, since growth of P. gingivalis occurred in the presence of ethylenediamine di-o-hydroxyphenylacetic acid provided haemin was added. Both apoLf and FeLf reduced haemin uptake by all three species and caused the release of cell-bound haemin in a dose-dependent manner. In addition, haemin reduced the binding of both apoLf and FeLf to P. intermedia and P. nigrescens but stimulated the binding of Lf by P. gingivalis. These data suggest that Lf forms complexes with haemin in solution and competes for the binding of haemin to certain cell receptors, possibly lipopolysaccharides, but this is not sufficient to inhibit growth of the bacteria. P. gingivalis appears to bind Lf-haemin complexes, as well as haemin alone, which may facilitate access of the Lf to the outer and cytoplasmic membranes of P. gingivalis, so disrupting function.