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Infect. Immun. doi:10.1128/IAI.01530-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

IsdA protects Staphylococcus aureus against the bactericidal protease activity of apolactoferrin

Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, United Kingdom

^* To whom correspondence should be addressed. Email: s.foster{at}sheffield.ac.uk.

	Abstract

An important facet of Staphylococcus aureus host-pathogen interaction, is the ability of the invading bacterium to evade host-innate defenses, particularly the cocktail of host antimicrobial peptides. In this work, we have shown that IsdA, a surface protein of S. aureus, which is required for nasal colonization, binds to lactoferrin, the most abundant anti-staphylococcal peptide in human nasal secretions. The presence of IsdA on the surface of S. aureus confers resistance to killing by lactoferrin. In addition, the bactericidal activity of lactoferrin was inhibited by addition of phenylmethylsulphonyl fluoride, implicating its serine protease activity in killing of S. aureus. Recombinant IsdA was a competitive inhibitor of lactoferrin protease activity. Reciprocally, antibody reactive to IsdA enhanced killing of S. aureus. Thus IsdA can protect S. aureus against lactoferrin, and acts as a protease inhibitor.

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