Human lactoferrin and peptides derived from its N terminus are highly effective against infections with antibiotic-resistant bacteria

Since human lactoferrin (hLF) binds to bacterial products through its highl y positively charged N terminus, we investigated which of the two cationic domains is involved in its bactericidal activity. The results revealed that hLF lacking the first three residues (hLF(-3N)) Was less efficient than hL F in killing of antibiotic- resistant Staphylococcus aureus, Listeria monoc ytogenes, and Klebsiella pneumoniae. Both hLF preparations failed to kill E scherichia coli O54. In addition, hLF(-3N) Was less effective than hLF in r educing the number of viable bacteria in mice infected with antibiotic-resi stant S. aureus and K. pneumoniae, Studies with synthetic peptides correspo nding to the first 11. N-terminal amino acids, designated hLF(1-11), and fr agments thereof demonstrated that peptides lacking the first three N-termin al residues are less effective than hLF(1-11) in killing of bacteria, Furth ermore, a peptide corresponding to residues 21 to 31, which comprises the s econd cationic domain, was less effective than hLF(1-11) in killing of bact eria in vitro and in mice having an infection with antibiotic-resistant S, aurveus or K. pneumoniae, Using fluorescent probes, we found that bacterici dal hLF peptides, but not nonbactericidal peptides, caused an increase of t he membrane permeability. In addition, hLF killed the various bacteria, mos t probably by inducing intracellular changes in these bacteria without affe cting the membrane permeability, Together, hLF and peptides derived from it s N terminus are highly effective against infections with antibiotic-resist ant S, aureus and K. pneumoniae, and the first two arginines play an essent ial role in this activity.