Niu, Yan D.Smith, Riley D.2023-05-112021-09-29Smith, R. D. (2021). Development of novel antimicrobials against avian pathogenic Escherichia coli that cause colibacillosis in laying hens (Master thesis). University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca .http://hdl.handle.net/1880/116460https://dx.doi.org/10.11575/PRISM/dspace/41304Avian pathogenic Escherichia coli (APEC) causes colibacillosis, a poultry disease which results in losses to the Canadian egg-industry. Colibacillosis in Canada cannot be treated with antibiotics due to Canadian Food Inspection Agency regulations, necessitating novel APEC control strategies. Phage biocontrol and tannin feed inclusion have been successful in reducing APEC infection in broiler chickens. We hypothesized that phages and tannins would be effective in treating colibacillosis in laying hens. The study objectives were to isolate and characterize anti-APEC phages for use in a laying hen model, test purple prairie clover (PPC) and brown seaweed (BSW) tannin efficacy against APEC in vitro and develop a laying hen APEC infection model for assessment of phage colibacillosis control. Phages targeting APEC strains were isolated from sewage and hen feces. The host range and lytic activity of seven isolated phages were determined using microplate phage virulence assays. Tannin efficacy was assessed using minimum inhibitory concentration (MIC) assays against APEC strains, and a laying hen APEC infection model was established via air sac APEC injection. Phages were subjected to transmission electron microscopy to determine morphology and pH tolerance assays were conducted to determine pH stability. Phage genomic DNA were extracted and sequenced via the Illumina MiSeq platform. Raw sequence reads were assembled and annotated via a variety of programs. To understand the relationship between the novel phages and their relatives, comparative genomic and proteomic analysis as well as phylogenetic trees were also conducted via standard programs. Four of seven phages possessed strong lytic activity against multiple APEC strains and phages were more stable between pH = 3.5 and 9.0 than at pH = 2.5. Whole-genome sequencing data showed there are four phages of the Myoviridae, one of the Autographiviridae, and two of the Siphoviridae families. PPC and BSW tannins both inhibited APEC growth in vitro (MIC < 150 µg/mL). The air-sac infection model was unsuccessful due to an insufficient infectious dose. Results show promise for the use of phages and tannins for the control of colibacillosis in laying hens.EnglishAvian pathogenic E. coliAPECBacteriophagesTanninsAntimicrobial ResistanceLaying henColibacillosisAgriculture--Generalmaster thesis