In order to determine which apoptotic pathway is stimulated by EspC during the infection of epithelial cells by EPEC, we quantified the activities of caspase-8 and caspase-9 by using their specific substrates, Ac-IETD-AFC (acetyl-Ile-Glu-Thr-Asp-7-amino-4-triflouromethylcoumarin) and Ac-LEDH-AFC (acetyl-Leu-Glu-His-Asp-7-amino-4-trifluoromethylcoumarin), respectively. Here, CASP9 is linked to infection.