Characterization of aStaphylococcus aureusSurface Virulence Factor That Promotes Resistance to Oxidative Killing and Infectious Endocarditis
ABSTRACTStaphylococcus aureusis a prominent human pathogen and a leading cause of community- and hospital-acquired bacterial infections worldwide. Herein, we describe the identification and characterization of theS. aureus67.6-kDa hypothetical protein, named for thesurface factor promoting resistance tooxidativekilling (SOK) in this study. Sequence analysis showed that the SOK gene is conserved in all sequencedS. aureusstrains and homologous to the myosin cross-reactive antigen ofStreptococcus pyogenes.Immunoblotting and immunofluorescence analysis showed that SOK was copurified with membrane fractions and was exposed on the surface ofS. aureusNewman and RN4220. Comparative analysis of wild-typeS. aureusand an isogenic deletion strain indicated that SOK contributes to both resistance to killing by human neutrophils and to oxidative stress. In addition, theS. aureus sokdeletion strain showed dramatically reduced aortic valve vegetation and bacterial cell number in a rabbit endocarditis model. These results, plus the suspected role of the streptococcal homologue in certain diseases such as acute rheumatic fever, suggest that SOK plays an important role in cardiovascular and other staphylococcal infections.