Resistance of viscous material-producing
strain OD1-16 against the phagocytic activity of human polymorphonuclear leukocytes
in vitro. P. intermedia OD1-16 cells were observed around the periphery of polymorphonuclear leukocyte but not internalized (A, arrow heads). In contrast, P. intermedia ATCC 25611 and Porphyromonas gingivalis ATCC 33277 cells without viscous material production were readily internalized and the ingested bacteria appear to be enclosed in cytoplasmic vacuoles (B and C, open stars). The data are representative from one of three independent experiments. Bars = 3.3 μm.