Raw animal by-products destined for rendering process may contain high population of harmful microorganisms including hydrogen sulfide-producing bacteria (SPB) and Salmonella. SPB are the spoilage bacteria that can utilize sulfur-containing compounds of raw animal by-products to produce hazardous gas-hydrogen sulfide (H2S) which is toxic. Salmonella may contaminate the rendered animal meals resulting in an introduction of human pathogens into the food chain. Furthermore, both SPB and Salmonella are likely to form biofilms on the various surfaces in rendering processing environment, serving as the source of recontamination and causing persistent microbiological safety problems. Therefore, novel and practical strategies to control these harmful bacteria need to be explored.;Bacteriophages are bacterial viruses that only infect specific species of bacteria without harming animals, plants and human, thus bacteriophage treatment has been explored as a novel biological method to control biofilms formed by persistent bacteria due to their high specificity and effectiveness. Therefore, the objectives of this study were: 1) to identify the sources of Salmonella contamination in rendering processing environment; 2) to optimize a scale-up production of Salmonella-specific bacteriophages; 3) to determine the effectiveness of bacteriophage treatment on reducing Salmonella and SPB attachment/biofilms on the surfaces under laboratory and greenhouse conditions; and 4) to apply bacteriophage treatment to reduce Salmonella and SPB attachment/biofilms on the surfaces in rendering processing environment.;For the first objective, a microbiological analysis of Salmonella contamination was conducted in two rendering plants in order to investigate the potential cross-contamination of Salmonella in rendering processing environment. Sampling locations were pre-determined at the potential areas where Salmonella contamination may occur including raw materials receiving, crax grinding and the finished meal loading-out areas.;For the second objective, a mixed bacteriophage production in a single batch was developed. To scale up the production of Salmonella-specific bacteriophages with low cost for field study (fourth objective). Bacteriophage titer of mixed bacteriophage production yielded 10.3 log PFU/ml with optimized conditions of multiplicity of infection (MOI) of 0.01, agitation speed of 200 rpm, nalidixic acid at concentration of 0.06 mug/ml and incubation time of 8 h at 37°C. Additionally, final titer of bacteriophage production could reach up to 11.5 log PFU/ml with a PEG-6000 precipitation at concentration of 8% and sodium chloride at concentration of 3%.;In the third objective, three SPB strains of Citrobacter freundii (n = 1) and Hafnia alvei (n = 2) were separately determined as strong biofilm formers using a 96-well microplate method. Application of 9 SPB-specific bacteriophages (107 PFU/mL) from families of Siphoviridae and Myoviridae resulted in 33-70% reduction of biofilm formation by each SPB strain. On stainless steel and plastic templates, bacteriophage treatment (108 PFU/mL) reduced the attached cells of a mixed SPB culture (no biofilm) by 2.3 and 2.7 log CFU/cm2 within 6 h at 30°C, respectively, as compared to 2 and 1.5 log CFU/cm 2 reductions of SPB biofilms within 6 h at 30°C.;For the fourth objective, our research on bacteriophage treatment of SPB and Salmonella was conducted in a rendering plant. For SPB application, indigenous SPB were allowed to form biofilms on the environmental surface, stainless steel, HDPE plastic, and rubber templates in a rendering plant for 7 days. A total of two trials were conducted for each season. With bacteriophage treatment (109 PFU/mL) for 6 h at room temperature, SPB biofilms were reduced by 0.7-1.4, 0.3-0.6 and 0.2-0.6 log CFU/cm 2 in spring, summer and fall trials, respectively.;In summary, our study examined the current contamination rates of Salmonella in rendered animal meals and rendering processing environment, and indicated the high potential of finished meals being recontaminated with Salmonella biofilms during the post-rendering process. We also optimized a scale-up production of mixed bacteriophages in a single batch with reduced cost for field application. Moreover, our study demonstrated that bacteriophages could reduce the selected SPB and Salmonella attachment/biofilms formed on various surfaces effectively, suggesting that the use of bacteriophages on the hard surfaces in rendering processing environment could control H 2S produced by SPB and Salmonella recontamination in rendered meals. Furthermore, the results of field study demonstrated the effectiveness of bacteriophage treatments in reducing indigenous SPB and Salmonella attachment/biofilms formed on the surfaces in rendering processing environment.;Overall, our research findings validated bacteriophage treatment as an effective, non-corrosive and environmentally friendly biological control method to reduce SPB and Salmonella attachment/biofilms in rendering processing environment, thereby, helping the rendering industry to have a safe working environment for workers and produce high quality rendered animal meals free from Salmonella contamination. (Abstract shortened by ProQuest.).
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