Detection of phages carrying the Shiga toxin 1 and 2 genes in waste water and river water samples

Aims: To evaluate the occurrence and abundance of phages that carry the stx(1) and stx(2) gene in water samples of different quality. Methods and Results: Phages growing on the Shiga toxin-negative Escherichia coli O157:H7 (ATCC 43888) strain were enumerated by a plaque assay in concentrated raw and treated waste water samples and river water samples. Plaques were investigated for the presence of stx(1) and stx(2) genes by a multiplex/nested PCR procedure. An overall number of 805 plaques were tested for the presence of stx-carrying phages. Stx genes could be demonstrated in 2% (stx(1)) and 16% (stx(2)) of the plaques. Stx-phages were eliminated with approximately the same efficiency in comparison with somatic coliphages during the waste water treatment process. Conclusions: Due to the low numbers of phages carrying the stx genes 1 and 2 in treated waste water and river water, the dilution and inactivation of host bacteria and the unsuitable conditions for the transduction of host organisms in aquatic environments, it is difficult to derive from the data the direct evidence for a public health problem. Significance and Impact of the Study: The results show the quantitative occurrence of stx-carrying phages in waste and river water and confirm the frequent circulation of these viruses in the aquatic environment.