Adherence to and entry of the parasite into the host is one of the essential elements of microbial pathogenicity. We investigated the adherence to and entry into primate kidney epithelial (Vero) cells of by radiolabelling techniques, immunofluorescence and electronmicroscopy. The attachment to and subsequent entry of both untreated and heat (50°)-treated into Vero cells occurred at cell-surface sites associated with aggregated coated pits. In contrast, there was minimal attachment of spirochaetes heated at 60°. Radiometric studies showed that, with untreated cells, there was incorporation of both C-glucose-1-phosphate and C-thymidine, whereas with the 50°-treated spirochaetes only glucose-1-phosphate was incorporated, and with the 60°-treated spirochaetes neither radionuclide was incorporated. Spirochaetes heated at 50° or 60° did not grow at 35° in culture medium. These results suggest that the presence of certain metabolic activities of the spirochaete but not viability (ability to grow) are necessary for the attachment process. After entry of untreated , most of the spirochaetes were either free in the cytoplasm or tightly bound to the host membrane. In contrast, 50°-treated spirochaetes remained bound to host membrane in large phagosome-like vesicles.


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