Doctor of Philosophy, The Ohio State University, 2018, Plant Pathology

Salmonellosis cases caused by Salmonella enterica through pre-harvest contamination of fresh produce represent a risk to human health worldwide; however, little is known about the interactions between Salmonella, phytopathogens, environment, and the plant host contributing to this food safety issue. Furthermore, the control of Salmonella from “farm to fork” is challenging due to the development of resistance mechanisms towards current control methods and restrictions on use of antimicrobials imposed by regulatory agencies. We investigated the effects of specific environmental conditions on the persistence and dissemination of Salmonella enterica subsp. enterica serotype Typhimurium (S. Typhimurium) following artificial contamination of `Tiny Tim' tomato plants. We found that higher temperatures (30°C day/25°C night) reduced the persistence of S. Typhimurium in the phyllosphere compared to lower temperatures (20°C day/15°C night) when plants were sprayed on the leaves with a S. Typhimurium -contaminated solution. Wounding cotyledons with contaminated tools increased S. Typhimurium persistence and internalization in planta compared to spray inoculation. Low relative humidity enhanced the dissemination of Salmonella into non-inoculated plant tissues. S. Typhimurium was detected in the root systems for at least 98 days-post inoculation. Further, we showed that splice-grafting (`Celebrity' with 'MaxiFort') is a major risk for the internalization and long-term survival of S. Typhimurium inside the tomato plant. S. Typhimurium was detected in the root system for over 137 days if at least 5 x 10^3 colony-forming units were introduced during grafting. The survival of S. Typhimurium in tomato foliage was also affected by the presence of phytopathogens, the genotype of S. Typhimurium and tomato variety used. We found that rfbV, involved in O antigen synthesis, might be essential for S. Typhimurium persistence in inoculated tomato plants and especially in `Tiny Tim' plants (open full item for complete abstract)

Committee: Gireesh Rajashekara (Advisor); Sally Miller (Advisor); Laurence Madden (Committee Member); Christopher Taylor (Committee Member); Corey Nislow (Committee Member) Subjects: Agriculture; Bioinformatics; Biology; Environmental Health; Molecular Biology; Plant Pathology; Public Health