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The goal of this research is to determine the influence of surface microstructure and composition on the attachment of bacterial pathogens to fruits and vegetables. <P>The relevant objectives from W1009 are to: (1) Adapt biological concepts associated with specialty crop production, harvest, and postharvest handling into quantifiable parameters which can be sensed. (2) Develop sensors and sensing systems which can measure and interpret the parameters.<P> The following outputs will be generated from activities on this research. Microfabrication methods will be developed to construct artificial surface structures on silicon which mimic natural plant surface structures on fruits and vegetables. From these artificial structures we will gain a better understanding of the exact role of microstructure on bacterial attachment. Methods will be developed to coat the artificial surfaces with materials similar to the natural plant cuticle, including waxes and polysaccharides. Tests with these coatings will give a better understanding of how surface hydrophobicity affects bacterial attachment. <P>These results will lead to improved understanding of the factors affecting bacterial contamination of fruits and vegetables, thereby leading to better methods for post-harvest washing and handling, as well as integration with sensors to detect contamination parameters.
Non-Technical Summary: Consumption of fresh vegetables contaminated with pathogenic bacteria has caused several large outbreaks of food-borne disease. The nature of bacterial attachment to plant surfaces has recently been studied to understand and ultimately prevent such contamination. Our research effort is to determine the effect of plant surface microstructure on bacterial attachment. Natural microstructures on plants come in uncontrolled sizes and shapes, which causes difficulty in understanding the exact effect of microstructure. Microfabrication techniques will be used to build structures on silicon surfaces with the desired dimensions and shapes into three general types; stomata, trichomes, and grooves between epidermal cells. Methods will be developed to coat the silicon surfaces with materials similar to natural plants, including paraffin for the cuticle wax and pectin for the outer cell wall. These artificial surfaces will be subjected to a culture of E. coli tagged with green florescent protein and observed under a confocal laser scanning microscope. Image processing will be used to quantify the location and level of attachment. The influence of microstructure type, size, and location on the tendency for attachment will be analyzed, and the effect of surface hydrophobicity will be determined. Ultimately we hope to better understand the physical factors and surface chemistry factors leading to attachment of bacterial pathogens to plant surfaces. This could lead to more effective methods for handling and washing fruits and vegetables. <P> Approach: Photolithography and basic microfabrication techniques will be used to construct microstructures on silicon which mimic structures found on natural plant surfaces, including trichomes, stomates, and ridges between cells. These structures will be coated with materials similar to those on natural plants, including paraffin wax to simulate the cuticle proper and pectin to simulate the polysaccharide fibrils of the inner cuticular layer. The artificial structures will be cultured in medium with labeled bacteria. The surfaces will be observed with a confocal laser scanning microscope. The patterns of bacterial attachment on the surface will be analyzed using image processing software. The effects of different surface microstructures and the confounding influence of surface material (hydrophobicity) on the likelihood of bacterial attachment will be determined. Post-harvest washing will be simulated using the artificial plant surfaces to develop more effective methods for washing and disinfecting fruits and vegetables.