FIG. 1.

Electron microscopy demonstrating the attachment and internalization of streptococci by human cultured pharyngeal cells. Bacteria were observed to associate with microvilli upon initial contact with the pharyngeal cells. Membrane extension is observed for the internalization process. Close observation indicates that surface proteins are involved with this initial interaction. Intracellular streptococci are found enclosed in cytoplasmic vacuoles with bacterial surface proteins still in contact with the membrane surface. The bacterial inoculum was prepared as described for the standard internalization assay. Magnification, ×12,700 (A) and 24,300 (B).