FIG. 6.

Effect of spore adherence inhibition on host cell infection. E. intestinalis spores (1, 5, 10, 50, or 100 million) were allowed to adhere to Vero host cells grown on glass coverslips in 12-well plates in the presence or absence of the adherence inhibitor chondroitin sulfate A (CSA). After 4 h of incubation, one set of coverslips from the 10-million-spore inoculum was removed to quantitate the inhibition of adherence (A). The remaining coverslips were washed to remove unattached spores and placed back in culture with normal medium for 30 h (B). Infected host cells were determined by visualizing developing intracellular spore clusters stained with propidium iodide as described in Materials and Methods. The percentage of infected host cells was calculated by dividing the mean number of infected cells per field of magnification by the mean total number of cells per field of magnification. Twenty random fields were counted for each data point. The asterisks indicate significant differences between chondroitin sulfate A-treated samples and nontreated samples (P < 0.0001). This experiment was repeated three times with similar results.