Quantitative assessment of the ability of Escherichia coli to invade cultured animal cells.

Assays to quantify bacterial invasion of epithelial cells generally fail to take account of the ability of the bacteria to adhere to the cells prior to invasion. We have developed a modified invasion assay to allow for this factor. We then used the assay to investigate diarrhoeagenic strains of Escherichia coli with differing ability to adhere to and invade HEp-2 epithelial cells. The results showed that enteroinvasive strains of E. coli were the most invasive variety, followed in order by enteropathogenic E. coli and enterotoxigenic E. coli. These findings correspond to what is known of the ability of the bacteria to invade the intestinal tract in vivo. The results also indicated that adhesins of diarrhoeagenic E. coli play no direct role in invasion, although they may facilitate invasion indirectly by promoting initial contact between bacteria and animal cells.