De Buck, JeroenHarman-McKenna, Victoria Katharine2023-10-262023-10-262023-10-24Harman-McKenna, V. K. (2023). Isolation, characterization, and application of novel bacteriophages for preventing experimental infection with Mycobacterium avium subspecies paratuberculosis (MAP) of dairy calves (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.https://hdl.handle.net/1880/117446https://doi.org/10.11575/PRISM/42289Johne's disease (JD), a chronic enteritis affecting ruminants, poses a substantial economic burden of $28 million CAD annually to the Canadian dairy industry. The disease is caused by Mycobacterium avium subsp. paratuberculosis (MAP) and primarily spreads to youngstock through the ingestion of contaminated feed and water. Due to JD's prolonged subclinical phase and the absence of a cure, conventional test-based culling has proven ineffective in curbing its spread. Mycobacteriophages, as potential anti-mycobacterial agents, offer promise in controlling mycobacterial infections. Isolating new MAP-lysing bacteriophages is a crucial step toward implementing phage-based JD control. In pursuit of novel mycobacteriophages for JD control, we optimized an isolation protocol involving fecal spiking and varied isolation solution compositions. This enhanced method led to a significant boost in phage yield, increasing it from less than 1% to an 59% recovery of the spiked phages from fecal samples. We screened 475 environmental samples, enriched with MAP and fast-growing M. smegmatis, sourced from farms with documented MAP presence. These samples encompassed diverse environments, including soil, manure pits, lactation barns, feces, milk, and drain water, resulting in the isolation of 14 phages. Restriction enzyme profiling facilitated the identification of 12 distinct and novel phages. Further investigations into host range revealed that 8 of these phages could lyse genetically diverse MAP strains. We also explored aspects such as cross-resistance, lysogeny, and the influence of pH. Subsequently, we assessed the efficacy of these mycobacteriophages in preventing MAP infection in dairy calves through oral administration in an experimental calf infection trial. This research demonstrated the potential of mycobacteriophages to prevent MAP infection effectively. Our findings highlight the discovery and characterization and application of eight novel mycobacteriophages. This research opens new avenues for the utilization of these newly isolated mycobacteriophages in strategies aimed at curbing the spread of Johne's disease on dairy farms.enUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.MycobacteriophagesPhage TherapyJohne's DiseaseVeterinary Sciencemaster thesis