PHENOTYPIC RESISTANCE TO THROMBIN-INDUCED PLATELET MICROBICIDAL PROTEIN IN-VITRO IS CORRELATED WITH ENHANCED VIRULENCE IN EXPERIMENTAL ENDOCARDITIS DUE TO STAPHYLOCOCCUS-AUREUS

Thrombin-induced platelet microbicidal protein (tPMP) is secreted by r abbit platelets following thrombin stimulation, and it kills common en dovascular pathogens in vitro, including Staphylococcus aureus, Theref ore, pathogens which exhibit tPMP resistance in vitro possess a potent ial survival advantage in vivo at sites of endovascular damage, We gen erated an isogenic S. aureus strain pair, differing in tPMP susceptibi lity, by transposon (Tn551) mutagenesis of a tPMP-susceptible (tPMP(s) ) parental strain (ISP479) to derive a stably tPMP-resistant (tPMP(r)) strain, ISP479R. ISP479 and ISP479R were equivalent in vitro in the f ollowing phenotypes: biotyping, antiobiograms, platelet adherence and aggregation, growth kinetics, cell wall-associated protein A expressio n, and fibrinogen binding, Genotypic comparisons of chromosomal DNA of strains ISP479 and ISP479R following restriction endonuclease digesti on revealed indistinguishable pulsed-field gel electrophoretic pattern s, The genotype exhibited by strain ISP479R was linked to the tPMP-res istant phenotype, as it was transducible into the initially tPMP-susce ptible parental strain, ISP479, Southern hybridization verified the pr esence of a single copy of Tn551 in the same chromosomal restriction s ite of both ISP479R and tPMP(r) transductants of ISP479, The correlati on of in vitro tPMP susceptibility phenotypes with the ability to indu ce experimental endocarditis (a prototypical endovascular infection) w as evaluated, Despite equivalent rates of endocarditis induction, anim als infected with strain ISP479R achieved significantly higher vegetat ion bacterial densities over a 7-day post-challenge period than did an imals infected with strain ISP479. These data suggest that tPMP(r) mic robial strains have a selective advantage in experimental staphylococc al endocarditis, Furthermore, the major impact of tPMP resistance upon endocarditis pathogenesis appears to involve a postvalvular adherence event(s), most probably by facilitating bacterial proliferation withi n vegetations.