Antibiotic resistance profile in chicken products and the efficacy of bacteriophage to control foodborne pathogens
A series of experiments was conducted to investigate the following issues: 1) the antibiotic resistance profile in bacteria isolated from chicken meat, 2) the development of a multivalent phage cocktail to control multiple Salmonella spp., 3) to determine the killing efficiency and characteristics of a Salmonella phage library, 4) to determine the efficacy of phage therapy in experimentally E. coli O157:H7 infected mice and its safety, and 5) to determine the genome sequence of one broad-spectrum Salmonella phage. The first study, presented in chapter two, characterized microbial contamination of chicken products from birds raised under different management conditions, conventional vs. antibiotic free. The overall bacterial contamination rates, foodborne pathogen contamination rates (Salmonella) and antimicrobial resistance profiles were also measured with standard microbiology protocols. This study suggested that eliminating on-farm use of antimicrobials does not reduce foodborne pathogen contamination, but does result in less contamination with antimicrobial resistant bacteria. The second study, presented in chapter three, consisted of the development and validation of a phage-based technology to reduce Salmonella colonization in food animals and increased host range to include serovars Typhimurium, Enteritidis and Kentucky. This study also developed a low-cost and effective means to microencapsulate the phage cocktail to allow for oral delivery. The third study, presented in chapter four, measured growth kinetics of phages that were previously shown to be effective in reducing Salmonella colonization in food animals. Meanwhile, the phage survivability under various preparation conditions including variations in pH and temperature, UV irradiation, fluctuations in temperature, desiccation and changes in ionic environment were also investigated. The results confirmed that temperatures greater than 87.5˚C, pH < 2.0, UV light (302nm and 365nm), chlorinated water (500 ppm) and microwaving inactivated tested phages. The forth study, presented in chapter five, aimed to determine whether phage-based technologies could limit E. coli O157:H7 without the concomitant increase in shiga toxin production and release. Phage therapy and antibiotic therapy were compared on the ability of control infection and the amount of shiga toxin release by E. coli O157:H7. In addition, the safety of phages was also investigated by measuring the immune response of mice against phage. The results suggested that phage therapy was similar to fosfomycin and ciprofloxacin in terms of antibacterial activity and shiga toxin 2 releases. This study also confirmed the safety of using phage therapy in vivo. The fifth study, presented in chapter six, announced the genome sequence of lytic Salmonella phage vB_SalM_SJ_3 which consisted of approximately 162,911 bp with a G+C content of 44.38%. The genome contained 210 predicted open reading frames (ORFs). The series of experiments showed the effects of antibiotic use on the antibiotic resistance of sentinel bacteria and pathogen load on the final meat products, as well as, the potential efficacy of phage therapy to replace antibiotic therapy in farm management settings.
Ebner, Purdue University.
Animal sciences|Animal Diseases
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