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Enhancing the inactivation of Escherichia coli O157:H7 by bacteriophage and gaseous ozone to improve postharvest fresh produce safety

Yesil, Mustafa
http://rave.ohiolink.edu/etdc/view?acc_num=osu1512103801957122

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Food Science and Technology.
Fresh produce is low in calories and high in the fibers, essential vitamins and minerals. Consumption of fresh fruits and vegetables helps prevention of cardiovascular diseases, cancer, diabetes and improves gastrointestinal health. Thus, fruit and vegetables have been gaining popularity among consumers and the increased consumption has been endorsed by many health organizations. On the contrary, fresh produce has continuously been associated with foodborne diseases outbreaks. It is technically challenging to decontaminate fresh produce due to the lack of microbial kill-step that effectively eliminate pathogens without causing product quality deterioration. Currently, chlorine wash is the most-used antimicrobial treatment of postharvest fresh produce. Gaseous ozone and bacteriophages have become popular as natural and environmental-friendly alternative decontamination technologies. Bacteriophages can be applied as alternative to chlorine spray or used as a final rinse before packing. Gaseous ozone was previously found very effective when combined with vacuum cooling to inactivate Escherichia coli O157:H7 on baby spinach. The objectives of this research were: (i) to evaluate the suitability of a single lytic bacteriophage, Escherichia phage OSYSP, as a fresh produce decontaminant; (ii) to assess the efficacy of bacteriophage OSYSP and gaseous ozone against E. coli O157:H7 on spinach leaves; and (iii) to develop a combination treatment involving bacteriophage and gaseous ozone to eliminate E. coli O157:H7 on spinach leaves. To justify using Escherichia phage OSYSP in fresh produce decontamination and other applications, the phage characteristics and genomic makeup were investigated (Chapters 2-4). The method to determine phage titer was optimized for maximum phage recovery and plaque clarity during enumeration. Stability of the phage at different incubation temperatures was investigated. The titer of a phage preparation did not change considerably during storage for up to 24 months at 4°C. Thermal resistance of the phage also was investigated. Interestingly, the bacteriophage OSYSP showed a remarkable heat resistance, compared to the host, Escherichia coli O157:H7 EDL933. These results suggest that bacteriophage OSYSP could be used in hurdle treatments for food products processed with mild heat. Complete sequencing of Escherichia phage OSYSP genome confirmed the presence of lysis-related genes and absence of undesirable virulence, lysogeny, allergenicity, and antibiotic resistance elements; these are desirable traits that confirm the suitability of OSYSP use as a biological control agent in food safety and therapeutic applications. One of the factors overlooked while designing new decontamination technologies is the role of pathogen load (microbial burden) on process efficacy. Therefore, decontamination of fresh produce with gaseous ozone was investigated as a function of product microbial load (Chapter 5). Spinach leaves were spot-inoculated with Escherichia coli O157:H7 at approximate initial populations of 108, 107, 105, and 103 CFU/g, and treated with a gaseous ozone during vacuum cooling. The treatment decreased Escherichia coli populations by 0.2, 2.1, 2.8, and >3 log CFU/g, respectively. Considering that natural contamination level of produce with pathogens is presumed to be low, the gaseous ozone treatment is considered efficacious against natural pathogen loads. Perishability of fresh produce necessitate the use of multiple mild hurdles to effectively eliminate infectious pathogens and decrease the risk of disease transmission. Therefore, combination of gaseous ozone and phage spray was investigated (Chapter 6). Spinach leaves were inoculated with 107 or 105 log CFU/g Escherichia coli O157:H7, and treated sequentially with alternating orders of gaseous ozone (during vacuum cooling) and phage spray. Treatment with gaseous ozone and bacteriophage decreased Escherichia coli O157:H7 populations by 1.8-3.4 and 1.7-3.4 log CFU/g, respectively. A sequential treatment of ozone followed by bacteriophage reduced the population of the bacterium by 5.2 log CFU/g. Additionally, survivors were not detected in spinach inoculated with the lower inoculum size and treated with ozone-phage combination. In conclusion, the study showed promising mild treatments that can be used in the fresh produce industry to control pathogens of concern. The presented intervention techniques could be easily integrated into conventional fresh produce processing with minimal modification of existing processing lines. Gaseous ozone treatment could be combined with currently-used vacuum cooling of freshly-harvested produce. The post-harvest chlorine spray and industrial chlorine-wash or rinse could be replaced with bacteriophage solution application.
Ahmed E. Yousef (Advisor)
V.M. Balasubramaniam (Committee Member)
Farnaz Maleky (Committee Member)
Jiyoung Lee (Committee Member)
231 p.
Food Science
Bacteriophage; Ozone; Fresh produce; Escherichia coli; Produce safety; Molecular characterization; Whole genome sequencing

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Citations

  • Yesil, M. (2017). Enhancing the inactivation of Escherichia coli O157:H7 by bacteriophage and gaseous ozone to improve postharvest fresh produce safety [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1512103801957122

    APA Style (7th edition)

  • Yesil, Mustafa. Enhancing the inactivation of Escherichia coli O157:H7 by bacteriophage and gaseous ozone to improve postharvest fresh produce safety. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1512103801957122.

    MLA Style (8th edition)

  • Yesil, Mustafa. "Enhancing the inactivation of Escherichia coli O157:H7 by bacteriophage and gaseous ozone to improve postharvest fresh produce safety." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1512103801957122

    Chicago Manual of Style (17th edition)

osu1512103801957122
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