The nature of the physical interactions between Escherichia coli JM109 and a model surface
(silicon nitride) was investigated in water via atomic force microscopy (AFM). AFM force
measurements on bacteria can represent the combined effects of van der Waals and
electrostatic forces, hydrogen bonding, steric interactions, and perhaps ligand− receptor
type bonds. It can be difficult to decouple these forces into their individual components since
both specific (chemical or short-range forces such as hydrogen bonding) and nonspecific …

For our measurements, μF and σF 2 were taken as the average and the variance,
respectively, of all of the pull-off forces measured on one cell (Table 1). A plot of σF 2 versus
μF is shown in Figure 3. The slope of the linear regression line that passes through the data
points shown in Figure 3 was taken to be the specific force, Fi, and the intercept was used to
calculate the nonspecific forces, Fo. It should be noted that both μ and σ2 in eqs 3 and 4 are
dimensionless.