In vitro endothelial cell damage is positively correlated with enhanced virulence and poor vancomycin responsiveness in experimental endocarditis due to methicillin-resistant Staphylococcus aureus

Abstract

SummaryThe pathogenesis of Staphylococcus aureus infective endocarditis (IE) is postulated to involve invasion and damage of endothelial cells (ECs). However, the precise relationships between S. aureus -EC interactions in vitro and IE virulence and treatment outcomes in vivo are poorly defined. Ten methicillin-resistant S. aureus (MRSA) clinical isolates previously tested for their virulence and vancomycin responsiveness in an experimental IE model were assessed in vitro for their hemolytic activity, protease production, and capacity to invade and damage ECs. There was a significant positive correlation between the in vitro EC damage caused by these MRSA strains and their virulence during experimental IE (in terms of bacterial densities in target tissues; P < 0.02). Importantly, higher EC damage was also significantly correlated with poor microbiologic response to vancomycin in the IE model (P < 0.001). Interestingly, the extent of EC damage was unrelated to a strain's ability to invade ECs, hemolytic activity and protease production, or β-toxin gene transcription. Inactivation of the agr locus in two MRSA strains caused ∼20% less damage as compared to the corresponding parental strains, indicating that a functional agr is required for maximal EC damage induction. Thus, MRSA-induced EC damage in vitro is a unique virulence phenotype that is independent of many other prototypical MRSA virulence factors, and may be a key biomarker for predicting MRSA virulence potential and antibiotic outcomes during endovascular infections.

Endovascular Infections Caused by Methicillin-Resistant Staphylococcus aureus Are Linked to Clonal Complex-Specific Alterations in Binding and Invasion Domains of Fibronectin-Binding Protein A as Well as the Occurrence of fnbB

“…FnBPs have been shown to promote bacterial adherence to and invasion of vascular endothelium in vitro (3,21,(30)(31)(32). Moreover, in vivo evidence supports the role of FnBPA as a virulence factor in experimental infective endocarditis (6,33).…”

“…PB isolates were obtained from patients demonstrating Ն7 days of positive blood cultures despite appropriate antibiotic therapy based on in vitro susceptibility profiles (20). RB isolates were obtained from patients in whom the initial bacteremia resolved within 2 to 4 days of antibiotic therapy (21,22). CC, clonal complex.…”

Reduced Vancomycin Susceptibility in anIn VitroCatheter-Related Biofilm Model Correlates with Poor Therapeutic Outcomes in Experimental Endocarditis Due to Methicillin-Resistant Staphylococcus aureus

“…The 10 MRSA bloodstream study isolates are listed in Table 1; these strains have been described in detail previously (15)(16)(17). All 10 strains had VAN MICs within the susceptible range (0.5 to 1.0 g/ml).…”

“…All 10 strains had VAN MICs within the susceptible range (0.5 to 1.0 g/ml). The five Rsp strains were defined as isolates in which VAN treatment caused a Ն5-log 10 CFU mean reduction per gram of vegetation and Ն3-log 10 CFU mean reduction per gram of kidney or spleen in a rabbit IE model (15,17). The five non-Rsp strains were defined as isolates in which Ͻ1.5-log 10 CFU mean reductions per gram of vegetation, kidney, and spleen were observed due to VAN treatment in the IE model (15,17).…”

“…The five Rsp strains were defined as isolates in which VAN treatment caused a Ն5-log 10 CFU mean reduction per gram of vegetation and Ն3-log 10 CFU mean reduction per gram of kidney or spleen in a rabbit IE model (15,17). The five non-Rsp strains were defined as isolates in which Ͻ1.5-log 10 CFU mean reductions per gram of vegetation, kidney, and spleen were observed due to VAN treatment in the IE model (15,17). To ensure that the phenotypic properties of these 10 strains were maintained upon long-term storage at Ϫ80°C, we retested a prototypic phenotype (delta-hemolysin production) (data not shown); this phenotype remained identical to those we previously described (15).…”