E. coli adhesion to silica in the presence of humic acid.

The influence of humic acid on the adhesion of Escherichia coli to silica particles or glass surfaces was investigated. After adsorbing various amounts of humic acid to the particles or surfaces, bacteria were added to the sample and allowed to adhere. For the silica particles the number of bacteria-particle couplets formed were counted from video microscopy images. For the glass surfaces, a differential electrophoresis force was applied, and the force required to detach the bacteria was quantified. These experiments showed a slight increase in the number of couplets formed in the presence of humic acid, and also showed a slight increase in the force required for detachment of the bacteria. Although an increase in adhesion number and strength was measured, the magnitude of the increase was small, indicating that humic acid plays a small role in bacterial adhesion to silica or glass surfaces.