FIG. 6.

Only P⁺ Opa⁺ organisms are found within HEC-1-B cells. TEM photomicrographs of HEC-1-B cells after 10 h of incubation with FA1090 P⁺ OpaE (A) and FA1090 P⁻ OpaE (B) organisms are shown. (A) Two cells are closely apposed, appearing as a single, ovoid cell. (Note the two nuclei, the tight junctions at the periphery, and microvilli in the space below the upper nucleus.) The lower (and larger) of the two cells contains what appears to be an internalized microcolony in which the individual cocci remain tightly adherent to each other; cocci may be in the process of being internalized into the upper cell. Vacuole membranes are not apparent around the ingested organisms. (B) Two cells are closely apposed, appearing as a single, ovoid cell. (Note the two nuceli, the tight junctions at the periphery, and the microvilli in the space between the nuclei.) The lower (and smaller) of the two cells contains a single internalized coccus, visible at the lower right; it appears to be within a vacuole. Other vacuoles within the cytoplasm are empty. (The “vacuoles” between the nuclei are intercellular spaces.) A second coccus is in close contact with the cell membrane. Bar, 1 μm.