The aggregation substance of Enterococcus faecalis increased bacterial adherence to and internalization by epithelial cells originating from the colon and duodenum but not by cells derived from the ileum. However, enterococcal translocation through monolayers of intestinal epithelium was not observed.Enterococcus faecalis, a gram-positive facultative anaerobic bacterium, belongs to the normal flora of the intestinal tract and is also found in the vaginal vault and the oral cavity. Enterococci have increasingly gained attention as pathogens, since they have become the fourth leading cause of nosocomial infections in the United States (8). E. faecalis frequently causes local or systemic infections, such as urinary tract and abdominal infections, wound infections, bacteremia, and endocarditis (15). It is assumed that many enterococcal infections are endogenous, resulting from bacterial translocation from the intestinal lumen to extraintestinal sites (16,31).Surprisingly little is known about the virulence factors of E. faecalis. One of the potential virulence factors is the aggregation substance (AS), an adhesin encoded by inducible sex pheromone plasmids (for a review, see reference 5). The AS, a signal peptide-containing protein, appears as a hair-like structure on the cell surface and is incorporated primarily into the ''old'' parts of the cell wall (30). It has been demonstrated that this adhesin is responsible for bacterium-bacterium contact during conjugative transfer of sex pheromone plasmids (5).The AS contains two Arg-Gly-Asp motifs which are known to be recognized by integrins, a family of eukaryotic cell surface receptors (24). Since integrins have been reported to be expressed on intestinal epithelial cells (2), we hypothesized that the AS promotes adherence and possibly invasion into these cells, thereby enabling enterococci to translocate through the intestinal epithelial barrier.(This work was presented in part at the 98th General Meeting of the American Society for Microbiology, Atlanta, Ga., 17 to 21 May 1998.)Three different E. faecalis strains (Table 1), kindly provided by R. Wirth (Institute of Microbiology, University of Regensburg, Regensburg, Germany), were used to study the effect of the AS on adherence, internalization, and translocation through intestinal epithelial cells. The bacteria were cultured in Todd-Hewitt medium (Difco, Augsburg, Germany) supplemented with erythromycin (20 g/ml) for growth of the plasmid-containing strains (OG1X/pAM721 and OG1X/pAM944). Since E. faecalis strains expressing the AS spontaneously clump, all inocula were sonicated (Branson W-450 Sonifier; 80 W, 20 s, continuously) to obtain single-cell suspensions. Salmonella enterica serovar Typhimurium ATCC 14028 and Escherichia coli HB101 grown in Luria-Bertani medium were used as positive and negative controls, respectively. For the experiments described below, the bacteria were harvested in mid-log phase and suspended in tissue culture medium without supplements, which served as the infection medium. Appropriate ...