Application of bacteriophages to control intestinal Escherichia coli O157:H7 levels in ruminants

A previously characterized O157-specific lytic bacteriophage KH1 and a newly isolated phage designated SH1 were tested, alone or in combination, for reducing intestinal Escherichia coli O157:117 in animals. Oral treatment with phage KH1 did not reduce the intestinal E. coli O157:117 in sheep. Phage SH1 formed clear and relatively larger plaques on lawns of all 12 E. coli O157:H7 isolates tested and had a broader host range than phage KH1, lysing O55:116 and 18 of 120 non-O157 E. coli isolates tested. In vitro, mucin or bovine mucus did not inhibit bacterial lysis by phage SHI or KHI. A phage treatment protocol was optimized using a mouse model of E. coli O157:117 intestinal carriage. Oral treatment with SHI or a mixture of SHI and KH1 at phage/bacterium ratios 2:102 terminated the presence of fecal E. coli O157:117 within 2 to 6 days after phage treatment. Untreated control mice remained culture positive for > 10 days. To optimize bacterial carriage and phage delivery in cattle, E. coli O157:117 was applied rectally to Holstein steers 7 days before the administration of 10(10) PFU SHI and KHI. Phages were applied directly to the rectoanal junction mucosa at phage/bacterium ratios calculated to be >= 10(2). In addition, phages were maintained at 10(6) PFU/ml in the drinking water of the phage treatment group. This phage therapy reduced the average number of E. coli O157:117 CFU among phage-treated steers compared to control steers (P < 0.05); however, it did not eliminate the bacteria from the majority of steers.