The pathogenicity of Salmonella was studied in different growth phases to clarify the VBNC state of this bacteria in the environment. Salmonella typhimurium in the logarithmic phase kills BALB/c mice much more efficiently than that in the stationary phase when infected p. o., and similar differences were observed in the binding activity of this bacteria in these growth phases to macrophages and colon epithelial cells. However, logarithmic Salmonella is more sensitive to distilled water than stationary Salmonella and did not survive longer than 2 days. On the contrary, stationary Salmonella survived for more than 8 months in phosphate-buffered saline and was able to regrow in nutrient-rich medium upon incubation at 37°C, showing pathogenic activity to mice.
Survey of Salmonella in the Tama River revealed that several colonies were virulent Salmonella enteritidis containing the plasmid encoding invA and enterotoxin, and some of these colonies showed lethality to mice as potently as pathogenic strains isolated from patients. These results suggest that Salmonella is found in river water and might regrow in nutrient-rich medium becoming pathogenic. Furthermore, the growth phase may be an important factor for this bacteria not only to survive in the environment but also to manifest pathogenicity to the host.
