1a. Objectives (from AD-416):
The objective of this cooperative research project is to elucidate mechanisms by which foodborne pathogens such as Escherichia coli O157:H7 may attach to and internalize in organic leafy greens and attach to equipment surfaces commonly used for harvesting and to evaluate the efficacy of alternative pre- and post-harvest interventions that can improve shelf-life and control pathogenic microbial growth and survival on organic leafy greens.
1b. Approach (from AD-416):
The general approach of this cooperative research project will determine the attachment and biofilm forming properties of E. coli O157:H7 on leafy greens. Surface charge and hydrophobicity measurements will be done and attachment will be viewed under confocal scanning laser microscope (CSLM). The role of curli and cellulose in attachment, internalization, and biofilm formation on organic leafy greens will be evaluated under a controlled environment. Leaf surface structure, leaf roughness, and 3-D image analysis of leaves of commonly used leafy green cultivars will be compared to evaluate pathogen attachment. Field experiments will be conducted as needed to determine the effect of cultivars on E. coli O157:H7 attachment on organic leafy greens. The efficacy of several plant derived antimicrobials will be evaluated in reducing or inactivating pathogenic and microorganisms on equipment used during harvest. Novel MBEC and CDC-bioreactor assays will be employed to evaluate biofilm removing capacity of natural antimicrobials.
3. Progress Report:
The internalization potential of E. coli O157:H7 (EHEC) into organic spinach roots and subsequent transfer to the edible portions of the plant were evaluated. The effect of curli (a bacterial surface appendage), spinach cultivar, and contamination level on EHEC internalization were also examined. Spinach cultivars Space and Waitiki were grown hydroponically under controlled conditions. After emergence of four true leaves, and hydroponics solution were inoculated with EHEC strains. Spinach leaves, stems, and roots were sampled after 0, 7, 14, 21 and 35 days to determine the incidence and populations of internalized bacteria. EHEC internalized into hydroponically-grown spinach roots and dispersed to the stem and leaf level. The internalization incidence was significantly affected by contamination level but not by curli expression or spinach cultivar.