Utilization of Aminosilane Antimicrobial Coatings in Spacecraft Potable and Technical Water Systems

Microbial control in spacecraft is currently achieved by environmental control of humidity, forced air filtration, and the use of antimicrobials for surface application (i.e., isopropyl alcohol) and biocidal agents for treatment of potable and technical water supplies (e.g., iodine and iodide or ionic and colloidal silver). Continuous monitoring is required to ensure water quality for shuttle and ISS missions. Water distribution systems for exploration missions on the Crew Exploration Vehicle (CEV) may benefit from a single-application surface-bound antimicrobial coating that limits microbial surface attachment. Consequently, we investigated the use of 3-(trimethoxysilyl) propyldimethyloctadecyl ammonium chloride, a commercially available quaternary aminosilane that bonds permanently to surfaces and inhibits microbial growth. To assess its suitability in spacecraft applications, we previously employed a test method to assess the effectiveness of aminosilane coatings on textiles. This method gave highly reproducible results showing as little as 0.1% aminosilane solution was effective in eliminating viable organisms from cloth swatches. The purpose of this study is to investigate the efficacy of an aminosilane coating for prevention of bacterial contamination of a potable water reservoir. Metallic coupons, composed of materials (i.e., Inconel 718, 21-6-9 Stainless Steel (aka, Nitronic 40), and 316 Stainless Steel) used in the construction of the Space Shuttle potable water distribution system, were treated with the antimicrobial, submerged into a volume of potable water, and inoculated with a known concentration of Burkholderia cepacia, a common bacteria isolated from Space Shuttle drinking water samples. The sample coupons were subjected to ultrasonic energy to re-suspend attached organisms. At various time-points, sample dilutions of inoculated potable water were plated on nutrient agar for enumeration of viable colony forming units. Reduction in the bacterial load and/or cell viability of bacteria in the reservoir was observed (less than 10 CFU/mL), providing support for the use of aminosilane coatings to prevent microbial contamination of spacecraft environmental systems.