Macroscopic adhesion-aggregation, floc formation, and subsequent transportation of microorganisms in porous media are closely related to the microscopic behavior and properties of individual cells. The classical Tabor's parameter in colloidal science is modified to correlate the macroscopic aggregation and microscopic adhesion properties of microorganisms. Seven bacterial strains relevant to wastewater treatment and bioremediation were characterized in terms of their macroscopic aggregation index (AI) using an optical method, and their microscopic coupled adhesion and deformation properties using atomic force microscopy (AFM). Single cells were indented to measure the range and magnitude of the repulsive-attractive intersurface forces, elastic modulus, thickness and density of the cellular surface substances (CSS). The strong correlation suggests that cost and time effective microscopic AFM characterization is capable of making reliable prediction of macroscopic behavior. (C) 2012 Elsevier Inc. All rights reserved.