Invasion of epithelial cells by aEPEC and tEPEC strains. A) Percent of invasion in HeLa cells. B) Percent of invasion in T84 cells. Monolayers were infected for 6 h (aEPEC) and 3 h (tEPEC). Results of percent invasion are expressed as the percentage of cell associated bacteria that resisted killing by gentamicin and are the means ± standard error from at least three independent experiments in duplicate wells. *significantly more invasive than prototype tEPEC E2348/69 (P < 0.05 by an unpaired, two-tailed t test).