The Fibronectin-Binding Protein EfbA Contributes to Pathogenesis and Protects against Infective Endocarditis Caused by Enterococcus faecalis

Abstract

EfbA is a PavA-like fibronectin adhesin of Enterococcus faecalis previously shown to be important in experimental urinary tract infection. Here, we expressed and purified the E. faecalis OG1RF EfbA and confirmed that this protein binds with high affinity to immobilized fibronectin, collagen I, and collagen V. We constructed an efbA deletion mutant and demonstrated that its virulence was significantly attenuated (P < 0.0006) versus the wild type in a mixed inoculum rat endocarditis model. Furthermore, efbA deletion resulted in diminished ability to bind fibronectin (P < 0.0001) and reduced biofilm (P < 0.001). Reintroduction of efbA into the original chromosomal location restored virulence, adherence to fibronectin, and biofilm formation to wild-type levels. Finally, vaccination of rats with purified recombinant EfbA protein protected against OG1RF endocarditis (P ‫؍‬ 0.008 versus control). Taken together, our results demonstrate that EfbA is an important factor involved in E. faecalis endocarditis and that rEfbA immunization is effective in preventing such infection, likely by interfering with bacterial adherence. E nterococci are among the first microbial colonizers of the infant gastrointestinal tract and, in healthy adults, they are part of the commensal intestinal microbiota (1). However, since the middle to late 1970s, enterococci have emerged as opportunistic pathogens and major causes of health care-associated infections, most notably urinary tract infections (UTIs) and bacteremia, second only to Staphylococcus spp. in the hospital setting (2-5). Among cases of enterococcal endocarditis, Enterococcus faecalis has been recognized as the most abundant species, accounting for more than 90% of isolates from this infection (2, 3, 6). Treatment of enterococcal endocarditis has been clinically challenging due to the emergence of strains resistant to commonly used antibiotics, i.e., aminoglycosides, although more recent use of ampicillin in combination with ceftriaxone seems to have alleviated this concern (7). The associated mortality remains high, with rates between 9 and 15% in Europe and the United States, respectively (8, 9).Adherence to and colonization of host tissue components, such as platelets and the extracellular matrix (ECM), are abilities that facilitate the early steps toward the development of infective endocarditis. To date, a variety of factors involved in the pathogenesis of experimental E. faecalis aortic valve infection have been identified; these include MSCRAMM (microbial surface components recognizing adhesive matrix molecules) proteins such as the adhesin to collagen, Ace, and the endocarditis and biofilm-associated pili, Ebp (10-12).Fibronectin is a glycoprotein consisting of two protein chains of approximately 250 kDa each, covalently linked by disulfide bonds, that is present in soluble forms in blood plasma and other body fluids. An insoluble, fibrillar form of fibronectin is present in the ECM and is known to support bacterial adherence (13). A recent study from Torelli et al. report...

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