[Wide occurrence of enterohemorragic Eschrichia coli O157 in natural freshwater environment].

Recent outbreaks of hemorrhagic colitis by Escherichia coli O157 urge us to clarify the source, distribution, and fate of those pathogens. We hypothesized that E. coli O157 enter into viable but nonculturable state (VBNC) so that the conventional culture method fails to detect those strains from natural environment. In the microcosm using sterilized river water, E. coli O157 gradually lost their viability. Total count using epifluorescent microscopy and the direct viable count (DVC), however, stayed almost constant for more than a month, indicating that the cells fell into the VBNC state. In order to see the distribution of E. coli O157 in natural environment, the DVC method and fluorescent antibody technique were applied. All river water samples from five different places in and near Tokyo metropolitan area showed occurrence of cells reacted with the antibody applied. This indicates that E. coli O157 may be widely distributed in freshwater environment as normal inhabitants. The understanding of VBNC state of E. coli O157 should be essential to investigate on the behavior of this pathogen in nature and find out a suitable method to prevent from further outbreaks.