EmaA, a Potential Virulence Determinant of Aggregatibacter actinomycetemcomitans in Infective Endocarditis

Abstract

The gram-negative fastidious human oropharyngeal Aggregatibacter actinomycetemcomitans is implicated in the etiology of infective endocarditis. EmaA, an oligomeric coiled-coil adhesin homologous to YadA of Yersinia enterocolitica, was hypothesized to mediate the interaction of A. actinomycetemcomitans with collagen. Collagen, the most abundant protein in human bodies and the main component of extracellular matrix (ECM), predominates in the supporting tissue of cardiac valves. To extend our earlier studies using purified collagen to determine bacterial binding activities, we developed a tissue model using rabbit cardiac valves to investigate the interaction of A. actinomycetemcomitans with native collagen. The resected mitral valves, with or without removal of the endothelium, were incubated with equivalent numbers of the wild type and the isogenic emaA mutant defective in collagen binding. There was no difference in binding between the wild-type and the mutant strains when the endothelium remained intact. However, the emaA mutant was fivefold less effective than the wild-type strain in colonizing the exposed ECM. A 10-fold increase in the binding of the wild-type strain to ECM was observed compared with the intact endothelium. Similar observations were replicated in an in vivo endocarditis rabbit model; the emaA mutant was 10-fold less effective in the initial infection of the traumatized aortic valve. Colocalization studies indicated that A. actinomycetemcomitans bound to type I collagen. A. actinomycetemcomitans preferentially colonized the ECM and, together with the evidence that EmaA interacts with the native collagen, suggested that the adhesin is likely a potential virulence determinant of the bacterium in the initiation of infective endocarditis.

Mitogen-Activated Protein Kinase 2 Signaling Shapes Macrophage Plasticity in Aggregatibacter actinomycetemcomitans-Induced Bone Loss

“…Aggregatibacter actinomycetemcomitans strain VT1729, serotype b, expressing the green fluorescent protein (obtained from the University of Vermont, Burlington, VT, USA) was originally derived from A. actinomycetemcomitans clinical isolate SUNY 465 (35). This serotype b strain was used in this study because of its high pathogenicity and high prevalence in periodontal disease in the United States (15,16).…”

“…This serotype b strain was used in this study because of its high pathogenicity and high prevalence in periodontal disease in the United States (15,16). Following previously described methods, A. actinomycetemcomitans was initially plated on 3% Trypticase soy broth and 0.6% yeast extract (TSBYE) 1.5% agar plates with 100 g/ml ampicillin (35). Aggregatibacter actinomycetemcomitans was then grown for 2 days in a 10% CO 2 incubator at 37°C and expanded in TSBYE broth containing 100 g/ml ampicillin overnight in 10% CO 2 at 37°C on a shaker.…”

Glycosylation of the Collagen Adhesin EmaA ofAggregatibacter actinomycetemcomitansIs Dependent upon the Lipopolysaccharide Biosynthetic Pathway

“…The competition assay was performed as described previously (45). Briefly, 1 ml of midlogarithmic-phase cells from the wild type and the rmlC mutant, equivalent to 2.5 ϫ 10 8 CFU in sterile PBS, was used for each assay.…”

“…The carboxyl termini of the proteins assume ␤-barrel structures required for pore formation and translocation of the molecules through the outer membrane, similar to those of other type V c autotransporter proteins (14). Recently, we have demonstrated that EmaA is important in the initiation of infective endocarditis in a rabbit model of infectious endocarditis (45).…”

Stick to Your Gums

“…The Aae and ApiA proteins promote attachment of A. actinomycetemcomitans to human buccal cells and GECs (Asakawa et al, 2003;Rose et al, 2003;Fine et al, 2005), while EmaA binds type I collagen, a mechanism also associated with the initiation of infective endocarditis (Tang et al, 2008) (Fig. 1).…”