The investigation was concerned with wild gram-positive and gram-negative microorganisms (E. coli spp., Klebsiella spp., Salmonella spp., and the nonfermentative bacteria Pseudomonas spp.) isolated from the waters of different types, as well as museum cultures (E. coli strain 1257, E. coli strain 675, Salmonella enteritidis ATCC 5765, Staphylococcus aureus 906, and Pseudomonas aeruginosa ATCC 10145). The wild strains were isolated from water when conducting experimental and field studies; these are able to survive in the waters disinfected by various procedures (a guanidine-containing disinfectant in non-toxic concentrations; photo-activated decontamination with sensitizers; exposure to magnetic and ultrasound waves). The cytotoxic, adhesive, and invasive activities of the bacteria isolated from environmental water objects increased on their cultivation on nutrient growth media, by simulating their possible effects in man. The developed experimental approach makes it possible to estimate the hazard of potentially pathogenic bacteria in one test trial, by applying the BGM cells and may be used to assess the microbial risk.