Atomic force microscopy (AFM) was used to probe heterogeneities in adhesion energies measured between pathogenic and non-pathogenic species of Listeria and silicon nitride in water at four levels. Adhesion energies were quantified on individual bacterial cells (cell level), bacterial cells that belonged to an individual Listeria strain but varied in their cultures (strain level), bacterial cells that belonged to an individual Listeria species but varied in their strain type (species level) and on bacterial cells that belonged to the Listeria genus but varied in their species type (genus level). To quantify heterogeneities in the adhesion energies, a heterogeneity index (HI) was defined based on quantified standard errors of mean. At the cell level, spatial variations in the adhesion energies were not observed. For the strain, species, and genus levels, the HI increased with increased adhesion energies. At the species level, the HI increased with strain virulence.
