Bacteria on the surface of river sand grains were successively detached by changing the number and strength of washing procedures and then divided into different fractions. The ratio of slow-growing organisms in each fraction increased as the number of washings increased and intensified by sonication. The cells of these slow-growing strains were more hydrophobic, less negatively charged and had greater isoelectric point (IEP) values compared with fast-growing strains. The strains having greater IEP values attached more easily to a glass and a plastic surface than the strains having smaller IEP values. These findings lead to an assumption that the slow-growing bacteria have surface characteristics enabling the cells to attach more firmly to substrate surfaces.