Microbial adhesion and retention on surfaces are complex phenomena, critical to the formation and development of biofilms. Recently, the focus of research has been more and more on the importance of retention of bacteria under fluctuating high shear forces in biofilm formation. The aim of the present work was to carry out a comparative study of the retention process of different bacterial and yeast species using: (1) a range of surfaces with different surface free energy properties and (2) a number of different bacterial cell physiological states. It was found for the first time that once a threshold cell number is retained on the surface, microbial retention patterns are formed following a power law, i.e., not stochastic. Our results demonstrated that the overall spatial patterns of microbial retention observed for the different substrates are similar for the all investigated cell types and that the drastic modification of the surface free energy does not affect this spatial organization. On the other hand, the microbial retention patterns appear to be significantly affected by the physiological state of the cells. Finally, the experimental retention patterns have been well simulated by a general agent-based model, confirming that the typical fractal distribution of retained cells is the result of a self-organization process. (C) Koninklijke Brill NV, Leiden, 2011