The interaction between Acanthamoeba polyphaga and human osteoblastic cells in vitro

Acanthamoeba spp. contains a group of free-living amoebae widespread in nature. These microorganisms may cause several diseases in humans including osteomyelitis. Here we characterize the cellular interaction between clinical and freshwater isolates of A. polyphaga with human osteoblasts. Amoeba cytoadherence was evaluated quantitatively and qualitatively. We observed that the clinical isolate readily adheres to human osteoblastic cells (HOB) in a saturable and time-dependent fashion. The cytoadhesion appears to be in part dependent on mannose-associated surface glycoconjugates, since prior incubation of the amoebae with alpha-mannose reduced cytoadhesion approximately 75%. Scanning electron microscopy revealed various amoebae exhibiting acanthapodia contacting the surface of osteoblasts. Some osteoblasts developed morphologies resembling apoptotic cells. The clinical isolate was highly toxic to HOB cells during 24 h of cell-protozoan interaction. Cytotoxicity was also dependent on the amoeba-cell ratio. During the cytopathogenic process we observed amoebae in the apparent process of ingestion of target cells and also amoebae extending projections or digipodia into osteoblast targets. The results indicate that A. polyphaga trophozoites attach and destroy human osteoblasts.