Aggregation properties of probiotics with pathogens are of importance for both food preservation and therapeutic impact of food on intestinal microbiota. We assessed spectrophotometry, fluorescence and radioactivity techniques to characterize and quantify co-aggregation. Probiotic strains tested showed co-aggregation abilities, which were strain-specific and dependent on time and incubation conditions. Co-aggregation may be useful for preliminary screening in order to identify potentially probiotic strains suitable for food, human or animal use.