Abstract
Direct cytotoxicity of black-pigmented Bacteroides was studied in the confluent monolayer of human gingival fibroblasts (HGF) in vitro. Only strains from Porphyromonas gingivalis caused morphological alteration (cell-rounding) and notable depression of viability of fibroblasts. This cytotoxicities were remarkably reduced by treating bacterial cells with acidic buffer (pH 3.5) at 37°C for 30 min. To determine the location of the cytotoxicity, bacterial surface components, i. e., outer membrane (OM), lipopolysaccharide (LPS) and outer membrane vesicles (OM-V) from P. gingivalis 381 were prepared and their cytotoxicity was assessed. The cytotoxicity of OM-V was found to be much stronger than that of the other two components, and this cytotoxic factor seemed to consist largely of protein and to be associated with the enzyme activity of OM-V. The effects of some protease inhibitors and L-cysteine on the cytotoxicity of OM-V suggest that the mechanism of cell-rounding is different from that of cell death.
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