Previous in vivo evidence has shown that bacterial phagocytosis by enterocytes may be an initial step in bacterial translocation across the intestinal epithelium. This study analyzed the interactions of cultured enterocytes, namely Caco-2 cells, with nine strains of enteric bacteria, tested in pure culture and in mixed culture. These nine strains had a spectrum of invasive potential and included Salmonella typhimurium, Listeria monocytogenes (three strains), Escherichia coli (three strains), Proteus mirabilis, and Enterococcus faecalis. Numbers of viable intracellular bacteria recovered from Caco-2 cells were: L. monocytogenes>S. typhimurium>P. mirabilis>E. coli>E. faecalis. Uptake of a given microbe by enterocytes was strain-specific and was not influenced by the presence of another strain, regardless of the invasive ability of the coinfecting strain. Electron microscopic visualization of bacterial adherence and uptake by Caco-2 cells indicated that the epithelial interactions of normal enteric bacteria were similar to these observed with invasive strains of salmonella and listeria.