Aggregation substance, a plasmid-encoded Enterococcus faecalis surface protein, plays a role in mediating the formation of mating aggregates, resulting in plasmid transfer. The role of aggregation substance in the internalization of E. faecalis by cultured intestinal epithelial cells, namely HT-29 cells, was analyzed. It was associated with a significant increase in endocytosis of E. faecalis by HT-29 cells: Numbers of internalized enterococci were fewer than of an invasive strain of Listeria monocytogenes, similar to Salmonella typhimurium and another L. monocytogenes strain, and greater than relatively noninvasive strains of E. faecalis, Proteus mirabilis, and Escherichia coli. Electron microscopy confirmed aggregation substance on the surface of strains interacting with the enterocyte microvillous surface, and intracellular enterococci were localized within membrane-bound vacuoles in the enterocyte cytoplasm. Thus, aggregation substance may facilitate E. faecalis internalization by host epithelial cells.
Bibliographical noteFunding Information:
Received 21 March 1994: revised 16 May 1994. Grant support: National Institutes of Health (AI-23484. AI-1931 O.GM-49530). Reprints or correspondence: Dr. Carol L. Wells. Dept. of Laboratory Medicine & Pathology. Box 198 UMHC. University ofMinnesota. Minneapolis. MN 55455. * Present affiliation: Lederle-Praxis Biologicals. West Henrietta. New York.