The contents of free sesquioxides are relatively high in acidic
soils (Table 2). The isoelectric point (pI) of Fe/Al (hydro) oxides is
much higher (8.5) than that ofE. coliO157:H7 (4.2)[30]. Hence,
in acidic soils, the Fe/Al (hydro) oxides carry net positive charges,
while the inoculatedE. coliO157:H7 were negatively charged. The
amount of positive charge on Fe/Al (hydro) oxides increased as
the pH decreased. Thus, the increase in the electrostatic attraction between the Fe/Al (hydro) oxides andE. colia celerated the