Macroscopic and nanoscale measurements of the adhesion of bacteria with varying outer layer surface composition

The influence of the lipopolysaccharide (LPS) chain length on bacterial adhesion was investigated by measuring the collision efficiencies of three Escherichia coli K12 strains, each having a different length LPS, to silica glass beads in column tests (macroscale tests). Nanoscale interactions between the bacteria and a silicon nitride tip were probed utilizing atomic force microscopy (AFM). Adhesion results based on column tests indicated that collision efficiencies of the three bacteria were not consistently correlated to LPS length. Under conditions of low ionic strength (1 mM NaCl), collision efficiencies increased with LPS length for the three strains of E. coli. However, if cells were fixed with glutaraldehyde (2.5%), the strain with the shortest LPS chain had the greatest adhesion, while the bacterium with the mid-length LPS had the least adhesion to glass beads. Collision efficiencies increased when the solution ionic strength was increased from 1 to 100 mM as expected, and in most cases glutaraldehyde treatment also increased adhesion. AFM force curves failed to distinguish the adhesion characteristics of these bacteria measured in column tests, as all AFM force curves on the bacteria were identical. Changes in adhesion were also not predictable by more conventional measurements of bacterial properties based on potential or contact angle. These results suggest that the LPS molecule length is not the sole determinant of adhesion of the three E. coli strains in porous media and that AFM force curve analysis, zeta potential, or contact angle data cannot yet be used to fully predict adhesion of these three strains to glass beads.