Abstract
Adhesion to host cells is an initial and important step in Acinetobacter baumannii pathogenesis. However, there is relatively little information on the mechanisms by which A. baumannii binds to and interacts with host cells. Adherence to extracellular matrix proteins, such as fibronectin, affords pathogens with a mechanism to invade epithelial cells. Here, we found that A. baumannii adheres more avidly to immobilized fibronectin than to control protein. Free fibronectin used as a competitor resulted in dose-dependent decreased binding of A. baumannii to fibronectin. Three outer membrane preparations (OMPs) were identified as fibronectin binding proteins (FBPs): OMPA, TonB-dependent copper receptor, and 34 kDa OMP. Moreover, we demonstrated that fibronectin inhibition and neutralization by specific antibody prevented significantly the adhesion of A. baumannii to human lung epithelial cells (A549 cells). Similarly, A. baumannii OMPA neutralization by specific antibody decreased significantly the adhesion of A. baumannii to A549 cells. These data indicate that FBPs are key adhesins that mediate binding of A. baumannii to human lung epithelial cells through interaction with fibronectin on the surface of these host cells.
Highlights
The ability of bacteria to interact with eukaryotic cells, leading to their own internalization, seems to be a critical event in the pathogenesis process of several microorganisms [1]
Soluble fibronectin used as a competitor was able to almost completely inhibit all three A. baumannii strains binding with an elective plasmatic fibronectin concentration inhibiting bacterial adherence at 50% (IC50) of
Western blotting analysis performed following 10% SDS-PAGE of outer membrane preparations (OMPs) of each A. baumannii strain (ATCC 19606, 77 and 113-16) and their transfer to nitrocellulose membranes revealed that incubation of this nitrocellulose membrane with fibronectin (10 mg/mL, 1 h) formed three stables complexes with fibronectin for each strain (Fig. 2A)
Summary
The ability of bacteria to interact with eukaryotic cells, leading to their own internalization, seems to be a critical event in the pathogenesis process of several microorganisms [1]. Acinetobacter baumannii have long been considered as nosocomial pathogen with low virulence. Several recent studies have shown that this microorganism is more virulent than expected [2]. Interaction between A. baumannii and the host epithelial cells is important in determining the outcome of infections. Various studies have shown that A. baumannii are able to adhere to and invade human epithelial cells; and induce epithelial cells death [3,4,5,6]. There is relatively little information on the mechanisms by which A. baumannii bind to and interact with host cells
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