SALMONELLA ON LEAFY GREENS IN A WARMING CLIMATE: ROUTE- AND TIMING-DEPENDENT PERSISTENCE, PREHARVEST BACTERIOPHAGE-BASED CONTROL, AND HORIZONTAL ANTIMICROBIAL RESISTANCE TRANSFER

Date

2025-11-07

Author

Namlı, Şahin

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Salmonella enterica is increasingly recognized as a food safety threat in fresh produce systems. This dissertation aimed to investigate how warming climate, contamination route, and timing influence Salmonella survival on leafy greens; whether preharvest bacteriophage application can serve as an effective biocontrol strategy; the bidirectional potential for antimicrobial resistance gene transfer involving Salmonella within plant-associated environments; and the role of the multidrug resistance megaplasmid pESI in shaping fitness within the plant environment. Controlled climate chamber experiments demonstrated that Salmonella can persist throughout the cultivation cycle, with late-stage irrigation posing the greatest risk. Single, well-timed phage applications near harvest were more effective in reducing Salmonella levels than multiple treatments starting earlier stages, which in some cases even diminished overall efficacy. Despite employing diverse mating assays -including in vitro, in planta, and biparental approaches- no horizontal gene transfer events were detected between Salmonella and environmental microbes or from Salmonella to co-inoculated Escherichia coli recipients, suggesting low horizontal gene transfer frequency under the tested conditions. The pESI plasmid, while advantageous in animal hosts, imposed a fitness cost in plants; competition assays revealed that plasmid-free strains outcompeted pESI carriers. Collectively, this work highlights the significance of contamination timing and route, the assessment of antimicrobial resistance transfer, and the necessity of preharvest interventions. It also emphasizes the influence of mobile genetic elements that may shift in response to the host environment. Furthermore, it elucidates the potential effects of a warming climate on both pathogen persistence and the likelihood of antimicrobial resistance transfer. Importantly, this study provides evidence-based insights and practical considerations to guide the development of effective mitigation strategies within fresh produce systems.

Subject Keywords

Salmonella enterica, leafy greens, climate change, bacteriophage biocontrol, antimicrobial resistance

URI

https://hdl.handle.net/11511/118313

Collections

Graduate School of Natural and Applied Sciences, Thesis