In vitro resistance to thrombin-induced platelet microbicidal protein in isolates of Staphylococcus aureus from endocarditis patients correlates withan intravascular device source

Platelet microbicidal proteins (PMPs) are small antimicrobial peptides secr eted by mammalian platelets. In vitro resistance of Staphylococcus aureus s trains to PMPs correlates with more extensive disease in experimental infec tive endocarditis (IE). To determine whether this same relationship exists in human S. aureus IE, we evaluated the in vitro PMP susceptibility phenoty pe of isolates from 58 prospectively-identified patients with definite S. a ureus IE. On multivariate analyses, patients with S. aureus IE complicating an infected intravascular device were significantly more likely to have IE caused by a PMP-resistant strain (P = .0193). No correlations were detecte d between in vitro PMP resistance among S. aureus strains and the severity of human IE. This work supports the concept that in vitro PMP resistance in clinical S. aureus strains is associated with important clinical character istics of S. aureus endovascular infections in vivo.