An official website of the United States government.
<OL> <LI> Improve our demonstrated nanoscale N-halamine surface functionalization methodology. Our current technology has been shown to regenerate antimicrobial N-halamine structures, but uses a wet chemical process for initial functionalization. We will explore UV irradiation for initial functionalization of polymer and stainless steel substrates. We will also investigate methods to increase the density of N-halamine forming moieties in order to increase antimicrobial activity. Finally, we will adapt our surface functionalization chemistries (successful on polyethylene) to perform on elastomeric (EPDM) and stainless steel substrates. <LI> Demonstrate repeated antimicrobial activity of the self-sanitizing food processing surfaces against food borne pathogens. Surfaces that have been functionalized with N-halamine nanostructures will be tested against isolates of E. coli, Vibrio spp., Salmonella spp., and L. monocytogenes to demonstrate the broad spectrum activity against a range of food borne pathogens. We will test antimicrobial activity of surfaces against cells in both planktonic and biofilm state.<LI> Establish the practical effectiveness of our rechargeable self-sanitizing food processing surfaces under stresses typical in a food processing environment. We will evaluate the effectiveness of our novel antimicrobial materials after long-term repeated use, after exposure to mechanical stress, and after contact with food components. Experiments will be performed to demonstrate that the covalently-linked N-halamine structures do not migrate from the surfaces during food production. Completing this objective will demonstrate the practical stability and activity of our N-halamine functionalized surfaces.
NON-TECHNICAL SUMMARY: Research in this project will design and characterize self-sanitizing processing surfaces through nanoscale surface modification. By making nanoscale changes to the surface of common materials, we introduce antimicrobial nanostructures, which can repeatedly recharge antimicrobial activity after rinsing in chlorine sanitizing solution. The resulting materials exert antimicrobial activity against a broad range of food pathogens and spoilage organisms. Materials regain antimicrobial activity during sanitization, making them practical for use in food processing environments.
<P>
APPROACH: Use ultraviolet light to functionalize gasket material and stainless steel. Introduce halamine containing moieties onto functionalized gasket and stainless steel substrates using a range of bioconjugation techniques. Alternate deposition of polyacrylic acid and polyethylenimine to increase the number of halamine moieties per unit area. Activate halamines by washing in dilute bleach (sodium hypochlorite). Quantify number of halamines by diethyl-p-phenylenediamine assay. Demonstrate long-term stability and rechargeability of halamine modified materials. Characterize surface morphology and chemistry of control and modified materials using infrared spectroscopy, atomic force microscopy, and scanning electron microscopy. Because of their prevalence in food borne disease, and because they represent both gram positive and gram negative organisms, E. coli, Vibrio spp., Salmonella spp., and L. monocytogenes will be used as challenge organisms in testing antimicrobial activity of the newly developed surfaces. At least two different strains of each organism will be tested, including isolates from a food processing environment and/or a food source when possible. We will obtain such isolates from the American Type Culture Collection (ATCC, Manassus, VA) as well as environmental isolates from the culture collection of Dr. Lynne McLandsborough (co-PI). Viability of microorganisms after contact with control and modified materials will be tested in both planktonic and biofilm form. Materials will be functionalized, wash in industrial sanitizers, and tested for halamine activation. This cycle of antimicrobial activity analysis, cleaning, and sanitization will be repeated up to 100 times. A Taber abrasion apparatus will be used to simulate repeated brushing of the N-halamine functionalized materials, per standardized test methodology ASTM D406079. Coupons of N-halamine modified EPDM or stainless steel will be placed on the abrasion apparatus, and an abrading wheel will be spun on the surface under a defined load. Unmodified materials will be similarly tested as a control. At intervals up to 5000 rotations, the materials will be removed and tested for N-halamine activity using the DPD assay described in Objective 1, as well as antimicrobial activity assays described in Objective 2. Roughness will be quantified at each interval using atomic force microscopy for nanoscale roughness and scanning electron microscopy for mesoscale roughness. As model food components, rolled oats, texturized vegetable protein, and coarsely chopped vegetables will be used. Coupons of N-halamine modified EPDM or stainless steel will be shaken in dry, sterile vials with the test food components for periods up to 6 hours. At 30-60 minute intervals, the materials will be removed and tested for N-halamine activity using the DPD assay described in Objective 1, as well as antimicrobial activity assays described in Objective 2. Unmodified materials will be similarly tested as a control.