Phagocytosis of non-opsonized Escherichia coli by mouse peritoneal macrophages. An electron microscopic study.

Phagocytosis of non-opsonized Escherichia coli by mouse peritoneal macrophages (MPM) was studied by means of light microscopy, scanning electron microscopy and transmission electron microscopy. During a phagocytosis period of 90 min the surface morphology changed. Early in the phagocytosis period the MPM were polar with many ridges and villi, and little ruffling. At the end of the period the cells appeared well spread with a smooth surface and extensive ruffling. Two modes for ingestion of bacteria seemed to exist. The bacteria were ingested either by membrane folds rising from the macrophage surface, fitting tightly to the bacteria or by bacteria sinking into the cytoplasm of the MPM. Early in the period of phagocytosis most bacteria were attached to the surface. Ten per cent of the bacteria attached were never ingested. Bacteria ingested were located in phagolysosomes that were either of a tight or a loose type. After a phagocytosis period of 90 min the phagolysosomes contained bacteria at different stages of degradation. During the degradation the bacteria showed several morphological changes including a decrease in the density of the endoplasm, detachment of the bacterial membrane from the cell wall and deformities in the bacterial cell wall.