Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2006
Publication Date: 9/1/2006
Citation: Raya, R.R., Varey, P., Oot, R.A., Dyen, M.R., Callaway, T.R., Edrington, T.S., Kutter, E.M., Brabban, A.D. 2006. Isolation and characterization of a new T-even bacteriophage, CEV1, and determination of its potential to reduce Escherichia coli O157:H7 levels in sheep. Applied and Environmental Microbiology. 72:6405-6410. Interpretive Summary: E. coli O157:H7 is a pathogenic bacteria that affects the beef industry. Nearly 1 out of 3 cattle test positive for carriage of E. coli O157:H7. Bacteriophage are viruses that specifically kill bacteria, and have been proposed for use as a method to reduce human exposures to E. coli O157:H7. In our study we isolated a naturally-occurring phage from sheep that was very active against E. coli O157:H7. Sheep were artificially inoculated with E. coli O157:H7 and were subsequently dosed with a single phage (CEV-1). Phage treatment reduced E. coli O157:H7 100-fold in the intestinal tract of the sheep. These results with a single phage indicate that phage therapy could be used to reduce pathogens in live animals. This application of phage therapy could significantly reduce the exposure of people to E. coli O157:H7.
Technical Abstract: Enterohemorrhagic Escherichia coli (EHEC), such as serotype O157:H7, are among today’s most prominent food-borne pathogens. About 28% of U.S. cattle presented for slaughter asymptomatically harbor E. coli O157:H7 and many human E. coli O157:H7 outbreaks have been linked to ruminants. In the present study, we describe the isolation and characterisation of a new virulent bacteriophage, CEV1, and explore its use in a potential intervention strategy to reduce the EHEC populations in ruminant animals. Phage CEV1 was isolated from a flock of sheep resistant to colonization by E. coli O157:H7. Electron micrographs and analysis of its main capsid protein (Gp23) showed it to belong to the T-even family and to be a close relative of T4. Molecular analysis showed that CEV1’s genome was 175~180 kb and also suggested that, like T4, it contains a modified nucleotide(s). In the lab under aerobic conditions CEV1 efficiently infected E. coli 0157:H7 (ATCC 12900) with a burst size of ~150 pfu/cell, an eclipse period of 18 min, and a latent period of 26 min. Similar efficient infection parameters were observed under anaerobic conditions. In vivo experiments, using a single oral dose of phage CEV1 in sheep to test the use of CEV1 as a preharvest intervention method, demonstrated a two-log reduction in the intestinal population levels of E. coli O157:H7 strain EDL 933 compared to the control. These results suggest that the use of bacteriophages as an intervention strategy could contribute significantly to reducing the incidence of human infection by E. coli O157:H7.