Tertiary models are established based on primary and secondary models and use predicted values of growth parameters from secondary models to predict changes in pathogen density at times and levels of independent variables that have not been tested or used in the model development .The survival of all three pathogens was longest in high-moisture and low-moisture dates at refrigerated temperature. The combination of their high pH values and low aw compared to the other dried fruits may be reasons why the dates have larger D-value than the other dried fruits. Juneja et al found that L. monocytogenes, E. coli O157:H7, and Salmonella spp. were able to survive on dates for 32 days when stored at 4 °C. Furthermore they found that there was no significant difference in any of the pathogens when the dates were treated with antimicrobial washes of peracetic acid or with ethanol . Because of this strong ability for pathogens to survive, Medjool dates should be further explored from a microbial safety viewpoint. The storage temperature had the biggest influence on decimal reduction time in Salmonella. While having the highest D values of the three pathogens in refrigerated dried fruit, Salmonella had the lowest D values in the dried fruit stored at ambient temperature . This shows that temperature has a large influence on the survival time of Salmonella. While thermal death time does increase for all three pathogens when put in colder conditions, the difference in Salmonella is the starkest. For example, according to the models made, the time is would take to reduce Salmonella by 90% in high moisture dates at refrigerated temperature would be 396 days, whereas at ambient temperature it would take 21 days . These results suggest that Salmonella has particularly increased survival at lower temperatures compared to other pathogens. While the specific mechanisms that allow for this survival in low moisture environments are not completely clear, garden pots square temperature most likely has an influence on those mechanisms. Andino and Hanning suggest one possible mechanism that Salmonella spp. may use to enhance its survival at lowered temperatures is cold shock proteins .

Upregulation of these proteins allow Salmonella to adapt to colder environments as temperatures drop, leading to better survival of the pathogen. Looking at the dried peaches , the decimal reduction time of the pathogens were higher when the peaches were inoculated with the dry carrier versus the wet carrier. This suggests that pathogens are more persistent when using a dry carrier to simulate a dry environment. However, a factor that might have influenced the lower D value in the wet inoculated peach is that the initial inoculation strength is several logs higher with a wet carrier than a dry carrier. Due to the higher initial microbial load in the wet inoculated peaches compared to the dry inoculated, there is difficulty in comparing the true impact that the wet and dry carrier had on the decimal reduction time.Dried fruit were inoculated with Salmonella spp., Escherichia coli, or L. monocytogenes to determine how they would survive in two storage conditions. All three pathogens were able to survive in dried fruits and should be taken into consideration when looking at the safety of dried fruit processing. Salmonella had the longest survival potential among all three tested pathogens. This observation is expected as Salmonella is known for its ability to survive in low moisture conditions. The condition that allowed for longer pathogens survival was storage at refrigerated temperature rather than ambient temperature. This is important because many dried fruit processors store their dried fruits at refrigerated temperatures if not being sold immediately. This allows for a longer shelf life of the dried fruit compared to ambient storage, but increases the ability for bacterial survival. This may be due to the intrinsic factors of the dried fruit: pH, aw, and available nutrient. Based on the current data, survival was the longest in the dried fruits that had the highest relative pH and the lowest relative aw. Salmonella inoculated in Medjool dates survived to the very end of the 180-day survival study.

The Medjool dates had the highest pH of all the dried fruits and had some of the lowest aw of the dried fruits. Other intrinsic factors that were not measured could have also played a role in the long survival time in the dates. For instance, dates are known to have a high sugar content, which may have played a role in pathogen survival. Measuring various compounds in the dried fruits might give more insight on why certain dried fruits allowed for longer survival than others. Regardless the reason, pathogen survival was long in Medjool dates, and should be something that those who produce dates consider. Since dates are not dried the same way other dried fruits are, the steps in the date harvesting process should be looked at carefully. While conducting this research, a new potential outbreak associated with Medjool dates was reported . Twenty-eight people in England were infected with Hepatitis A in 2021 and is suspected to be from Medjool dates . The dates have since been recalled due to their possible contamination . In 2018 there was another outbreak of Hepatitis A in Denmark and was believed to be from dates from Iran . There has been no evidence to show that those dates were contaminated with the virus . That potentially makes this 2021 outbreak the first to be associated with a dried fruit not part of a mixed product. With the occurrence of this outbreak, it makes it all the more important to understand when and where potential contamination of pathogens in dried fruits can occur. Although the data generated from our study is based on bacteria, we did see that the survival of pathogens in Medjool dates is longer compared to other dried fruits. Additional research will be necessary to better understand the survival of foodborne virus on dried fruits. As discussed earlier in this thesis, there are many pre- and post-drying treatments that can be applied to fresh or dried fruits. When looking into the available literature, the efficacy of these treatments has not been systematically evaluated. One on-going project in the lab is to summarize the current knowledge about these treatments and their efficacies and develop a study that fills in the knowledge gaps. In the meantime, identifying a surrogate for testing the different pre- and post-drying treatments as well as different drying methods is needed.

Enterococcus faecium NRRL B-2354 has been validated and approved for being used as a surrogate for almond thermal processing validation . However, whether this strain can be as a surrogate for dried fruit related studies or not still needs further evaluation. One on-going test project in the lab is go evaluate the survival of E. faecium NRRL B-2354 in dried peaches and apricots. In this first test trial, E. faecium was inoculated onto two types of dried fruits and its survival at ambient and refrigerated temperatures is being monitored. In addition, the highest temperatures that can be achieved by various dry methods are being monitored and recorded. The efficacy of different pre-drying treatments is also being tested in the lab by using Salmonella-inoculated peaches and E. faecium-inoculated peaches. In summary, the microbial safety of dried fruits is important and needs more research attention. The survivability of common foodborne pathogens on different types of dried fruits and the recalls and outbreaks associated with dried fruits highlight the importance of the validation of pre- and post-drying treatments as well as different drying methods. The findings of this study, square pots along with future work, hopes to provide the foundation needed for the development of food safety plans for dried fruits.Under global warming and climate change, cultivated plants are encountering increased biotic and abiotic stresses, which lead to reductions of plant growth and reproduction and consequently economic losses. The use of plant endophytic bacteria to promote plant growth and increase tolerance of environmental stresses has provided an alternative to standard agricultural practices that has fewer safety concerns. Endophytic bacteria can be defined as non-pathogenic bacteria that colonize the interior of host plants and can be isolated from surface-sterilized plant tissues. These bacteria can obtain a constant nutrient supply from host plants by living inside the plants and having close contact with plant cells. The endophytic bacteria colonization process is usually initiated at wounds and cracks in the roots by a rhizospheric population of the bacteria in the soil. After entering the plant roots, endophytic bacteria can systemically colonize the above ground parts of plants, including stems and leaves.A wide diversity of endophytic bacteria has been discovered in several plant species. Endophytic bacteria communities include five main phyla. Proteobacteria is the most dominant phylum isolated from host plants, which includes α-, β-, and γ-Proteobacteria. Actinobacteria, Planctomycetes, Verrucomicrobia, and Acidobacteria are also commonly identified. The most frequently isolated bacteria genera are Bacillus, Burkholderia, Microbacterium, Micrococcus, Pantoea, Pseudomonas, and Stenotrophomonas, with the two major genera being Bacillus and Pseudomonas. Several factors affect the composition of endophytic bacteria populations, including plant growth conditions, plant age, types of analyzed plant tissues, soil contents, and other environmental factors. Endophytic bacteria can have several beneficial effects on host plants, such as promotion of plant growth and yield, increased resistance to plant pathogens, enhanced tolerance to abiotic stresses, elimination of soil pollutants through the facilitation of phytoremediation, and production of various metabolites with potential applications in agriculture, medicine, and industry. Some endophytic bacteria help host plants acquire increased amounts of limited resources from the environment. This can include enhancing the uptake of nitrogen, phosphorous, or iron by expressing nitrogenase, solubilizing precipitated phosphates, or producing iron-chelating agents in bacteria, respectively. Some endophytic plant-growth-promoting bacteria can increase host plants’ metabolism and nutrient accumulation by providing or regulating various plant hormones, including auxin, cytokinin, gibberellins, or ethylene. Auxin and ethylene are the two major hormones that affect plant growth and development and that are involved in plant-endophytic bacteria interactions. In addition to these four hormones, several endophytes can utilize signaling pathways mediated by salicylic acid, jasmonic acid, and ethylene to initiate induced systemic resistance and protect host plants from phytopathogen infection. A number of endophytic bacteria can also produce various antibiotics, toxins, hydrolytic enzymes, and antimicrobial volatile organic compounds to limit pathogen infection. We previously isolated a plant endophytic bacterium, Burkholderia sp. strain 869T2, from surface-sterilized root tissues of vetiver grass. Strain 869T2 can also live within banana plants, in which it promoted growth and reduced Fusarium wilt disease occurrence. Genomic sequences of the strain 869T2 contain the gene for 1-aminocyclopropane-1-carboxylate deaminase, which may modulate host plant ethylene levels. Strain 869T2 also has genes related to the synthesis of pyrrolnitrin, which may function as a broad-spectrum anti-fungal agent, as well as dioxin-degradation-related genes. Furthermore, strain 869T2 can degrade the toxic dioxin congener 2,3,7,8-tetrachlorinated dibenzo-p-dioxin , mainly via its 2-haloacid dehalogenase. A recent study compared the genome sequences of 31 Burkholderia spp. and reclassified Burkholderia cenocepacia strain 869T2 as Burkholderia seminalis. We also compared the genome sequences of the strain 869T2 with those of five published B. seminalis strains: FL-5-4-10-S1-D7, FL-5-5-10-S1-D0, Bp9022, Bp8988, and TC3.4.2R3. The strain 869T2 shared 93–95% of its genome with the other five B. seminalis strains. Furthermore, strain 869T2 lacked several genetic loci that are important for human virulence. Based on the results of our analysis of the core genome phylogeny and whole-genome average nucleotide identity , strain 869T2 was classified as B. seminalis. B. seminalis is a member of the Burkholderia cepacia complex , which is a group of Gram-negative, aerobic, non-sporulating, rod-shaped bacteria. Bcc consists of opportunistic human pathogens that exist in patients suffering from cystic fibrosis as well as pathogens of many vegetables and fruits, such as onion and banana. Contrary to the pathogenic traits that led to their original discovery, some Bcc bacteria have ecologically beneficial interactions with host plants. The plant endophytic bacterium B. seminalis strain TC3.4.2R3, isolated from sugarcane, can serve as a biocontrol agent to reduce infections with Fusarium oxysporum and the cacao pathogens Moniliophthora perniciosa , Phytophthora citrophtora, P. capsici, and P. palmivora as well as orchid necrosiscaused by Burkholderia gladioli through the production of pyochelin, a rhamnolipid, and other unidentified diffusible metabolites. Another strain of Burkholderia seminalis, strain R456 isolated from rice rhizosphere soils, decreased the occurrence of rice sheath blight disease caused by Rhizoctonia solani.