Effect of bacteriophage DC22 on Escherichia coli O157:H7 in an artificial rumen system (Rusitec) and inoculated sheep

The effect of a bacteriophage, DC22, on the survival of Escherichia coli O157:H7 in an artificial rumen system (Rusitec) and in experimentally inoculated sheep was assessed. Plaque assay challenge of E. coli strains to DC22 showed that 23 of 23 E. coli O157:H7 strains were sensitive to DC22, while 12 non-O157 strains of enterohemorrhagic E. coli were not sensitive to the bacteriophage. In triplicate studies using clarified ruminal fluid, the multiplicity of infection (MOI) of DC22 on E. coli O157:H7 was determined to be >10(4) plaque forming units (PFU)/CFU. In the artificial rumen system (Rusitec), 10(4) CFU.mL(-1) of E. coli O157:H7 strain 3081 were eliminated from the fermenters (n=4) 4 h following the administration of 10(5) PFU of DC22/CFU of E. coli O157:H7 (P<0.05). Escherichia coli O157:H7 persisted in the control fermenters (n=4) for up to 168 h post-inoculation. Two groups of six wether lambs were fasted for 48 h and orally inoculated with 10(8) CFU of E. coli O157: H7 strain E318N. On day 2 post-inoculation, one group was inoculated with 10(5) PFU/CFU of DC22 (DC22-treated group) and the other group was inoculated with an equivalent amount of SM buffer (control group). There was no difference (P>0.05) in the levels of E. coli O157:H7 shed by lambs in the DC22-treated group or control group over a 30 day period. Levels of DC22 recovered from the feces of the DC22-treated group declined from 5.98 log(10) PFU.g(-1) on day 3 to undetectable in all lambs on day 13. Non-specific adsorption of DC22 or inactivation prior to reaching the lower tract may have reduced its effectiveness at eliminating E. coli O157:H7 from the intestinal tract of lambs.