Settling profile assays. The numbers in parentheses indicate the final optical density of the bacterial suspension after homogenization. A- Settling profile displayed by EACF 205 and EAEC strains. Bacterial aggregates were formed only when EACF 205 was mixed with traA-positive EAEC strain 340-1 or 205-1. B- Effect of zinc on the settling kinetic developed by EAEC strain 340-1 or 205-1 in the presence of EACF 205. C- SEM micrograph showing non-bundle forming, flexible pili (white arrow) mediating the formation of EACF-EAEC aggregates. Pili extend away from bacteria up to 2 μm, connecting other bacteria.