Comparative survival of free Shiga toxin 2-encoding phages and Escherichiacoli strains outside the gut

The behavior outside the gut of seeded Escherichia coli O157:H7, naturally occurring E. coli, somatic coliphages, bacteriophages infecting O157:H7, an d Shiga toxin 2 (Stx2)-encoding bacteriophages was studied to determine whe ther the last persist in the environment more successfully than their host bacteria. The ratios between the numbers off. coli and those of the differe nt bacteriophages were clearly lower in river water than in sewage of the a rea, whereas the ratios between the numbers of the different phages were si milar. In addition, the numbers of bacteria decreased between 2 and 3 log u nits in in situ survival experiments performed in river water, whereas the numbers of phages decreased between 1 and 2 log units. Chlorination and pas teurization treatments that reduced by approximately 4 log units the number s of bacteria reduced by less than 1 log unit the numbers of bacteriophages . Thus, it can be concluded that Stx2-encoding phages persist longer than t heir host bacteria in the water environment and are more resistant than the ir host bacteria to chlorination and heat treatment.