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TRANSFER MECHANISM AND TRANSCRIPTOMIC PROFILING OF SALMONELLA IN FRESH-CUT FRUITS
Title
TRANSFER MECHANISM AND TRANSCRIPTOMIC PROFILING OF SALMONELLA IN FRESH-CUT FRUITS
Creator
Chen, Ruixi
Date
2018, 2018-05
Description
Salmonella has been recognized as an increasing concern for food safety of fresh fruits because of their constant involvement in associated...
Show moreSalmonella has been recognized as an increasing concern for food safety of fresh fruits because of their constant involvement in associated foodborne outbreaks. However, knowledge is relatively limited about the transfer pattern of this particular pathogen from contaminated to uncontaminated fruits, nor do we know about the molecular mechanisms incorporated by it to address the environment of fresh fruits. In this study, we investigated the transfer mechanism of Salmonella enterica serovars Newport and Typhimurium between fresh gala apples and cantaloupes, respectively, via consecutive fresh cuttings and the subsequent survival of the strains in juice and cube fruit products under 4oC for up to 7 days. We also used RNA-seq and bioinformatics approaches to explore the transcriptome of Salmonella Newport in cantaloupe in comparison with 0.1% BPW (control group). Our results demonstrated fresh cutting as a practical way for bacterial transfer from contaminated to up to 4 uncontaminated fruits, and the transfer rate decreased drastically as the number of fresh cuts increased. The relative distribution of Salmonella cells in the 1st un-inoculated cantaloupe sample was significantly higher than the corresponding gala apple sample (p ≤0.05), while the transfer rate to the following un-inoculated samples in the cantaloupe group was visibly lower than the gala apple group. In general, cantaloupe, rather than gala apple, was capable to at least maintain a constant level of bacterial population during the 7 days storage at 4oC, with juice sample being even more supportive than cube sample (p ≤0.05). Moreover, Salmonella Typhimurium had a better adaptation in cantaloupe environment than Salmonella Newport. According to the results of transcriptome analysis, metabolism activities were promoted for essential nutrient requirements including carbon, energy, nitrogen, phosphorus, iron and zinc comparing to the control group, while suppressed for others such as lipid and fatty acids (FDR ≤0.05, |log2 FoldChange| ≥1). The differential regulation of the corresponding genes of the biological processes was possibly achieved in a time much less than 1 hour.
M.S. in Food Safety and Technology, May 2018
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Efficacy and Mechanisms of Power Ultrasound-Based Hurdle Technology for Reduction of Pathogens in Fresh Produce
Title
Efficacy and Mechanisms of Power Ultrasound-Based Hurdle Technology for Reduction of Pathogens in Fresh Produce
Creator
Zhou, Xinyi
Date
2023
Description
Minimally processed produce is frequently contaminated with foodborne bacterial pathogens. Power ultrasound is a non-thermal and cost...
Show moreMinimally processed produce is frequently contaminated with foodborne bacterial pathogens. Power ultrasound is a non-thermal and cost-effective technology that can be combined with other chemical sanitization methods. This study investigated the reduction of Listeria monocytogenes and Salmonella Newport on grape tomato, romaine lettuce, and spinach washed with water, chlorine, or peroxyacetic acid alone or in combination with 25 or 40 kHz power ultrasound for 1, 2, or 5 min. Produce items were inoculated with selected pathogens at approximately 10 log CFU/g, air dried for 2 h, and then treated. Combined treatment of ultrasound and sanitizers resulted in 1.44-3.99 log CFU/g reduction of L. monocytogenes and 1.35-3.62 log CFU/g reduction of S. Newport on washed produce items, with significantly higher reductions observed on grape tomato. Synergistic effects were achieved with the combined treatment of power ultrasound coupled with the chemical sanitizers when compared to the single treatments. An additional 0.48-1.40 log CFU/g reduction of S. Newport was obtained with the combined treatment on grape tomato. In general, no significant differences (p<0.05) were observed in pathogen reductions between the selected ultrasound frequencies, sanitizers, or treatment lengths. Results from this study suggest that incorporation of power ultrasound to current treatment can enhance bacterial pathogen reduction on fresh produce surface, but cannot completely eliminate bacterial pathogens. Transcriptomic study revealed significant (|Log2 fold change|<1 and false discovery rate < 0.05) transcriptional changes in L. monocytogenes LS810 in response to the 2 min power ultrasound treatment. The up-regulation of genes encoding TPI, LLO, and PTS indicates increased energy requirements, enhanced virulence, and demand for sugar sources in bacteria. On the other hand, the down-regulation of genes involved in cyclic dimeric GMP hydrolysis and transcriptional regulation suggests a modulation of intracellular signaling, cellular processes, and metabolisms to enhance survival and recovery. The GO and KEGG analysis demonstrated defense mechanisms against ultrasound stress more comprehensively. L. monocytogenes adjusts its metabolism, repairs cell membranes, and conserves energy for survival. These findings enhance our understanding of its adaptation to environmental stress. Results of this study can be used as a start point for optimizing the efficacy of ultrasound-based hurdle treatments for fresh produce disinfection.
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