Inducible expression of Enterococcus faecalis aggregation substance surface protein facilitates bacterial internalization by cultured enterocytes

Aggregation substance (AS) is an Enterococcus faecalis surface protein that may contribute to virulence. Using a recently described system for control led expression of AS in E. faecalis and the heterologous host Lactococcus l actis, experiments were designed to assess the effect of AS on bacterial in ternalization by HT-29 and Caco-2 enterocytes. AS expression was associated with increased internalization of E. faecalis by HT-29 enterocytes and of L. lactis by HT-29 and Caco-2 enterocytes. Compared to enterocytes cultivat ed under standard conditions, either cultivation in hypoxia or 1-h pretreat ment of enterocytes with calcium-free medium resulted in increased internal ization of both E. faecalis and L. lactis (with and without AS expression). Also, AS expression augmented these increases when E. faecalis was incubat ed with pretreated HT-29 enterocytes and when L. lactis was incubated with pretreated Caco-2 and HT-29 enterocytes. These data indicated that AS might facilitate E. faecalis internalization by cultured enterocytes.