Alterations in cell morphology and cytoskeletal proteins in gingival fibroblasts exposed to a Bacteroides gingivalis extract.

A soluble sonic extract (SSE) from Bacteroides gingivalis caused a dose-dependent inhibition of gingival fibroblast growth, reduced cell attachment and altered cell morphology. Most of its cytotoxic activity was destroyed by heating, indicating that the factor(s) was a protein rather than endotoxin. Cells, grown in the presence of, or on, root surfaces pretreated with 100-200 micrograms SSE/ml, partially retracted from the substratum and exhibited extensive surface blebbing and finger-like protrusions. Immunofluorescent staining showed that the morphological effects of Bacteroides gingivalis SSE are directed specifically at actin stress fibers and not microtubules of the cytoskeleton. Exposure to the SSE resulted in a dramatic relocalization of the bulk of F-actin from a fibrous form to a non-aggregated diffuse form. Disorganization of actin stress fibres occurred at concentrations of SSE that inhibited cell growth, but preceded any observable changes in cell attachment or morphology. The microtubular network remained intact, although it stained less intensely than that of controls. By contrast, Bacteroides intermedius SSE did not significantly influence growth, alter cellular morphology or affect the two cytoskeletal proteins.