Sampling wipes were prepared at the Jet Propulsion Laboratory (JPL; Pasadena, CA). Briefly, each polyester wipe (9″ × 9″; ITW Texwipe, Mahwah, NJ) was folded two times and soaked in 15 mL of sterile molecular grade water (Sigma-Aldrich, St. Louis, MO) for 30 min followed by the transfer to a sterile zip lock bag [73 ]. The sampling kit was assembled at NASA Ames Research Center (ARC, Moffett Field, CA). The implementation team at NASA ARC delivered the kit to the Cargo Mission Contract at Johnson Space Center (Texas) which was then transferred to Kennedy Space Center (Florida) in order to be loaded into the Space Exploration Technologies (SpaceX) Dragon spacecraft prior to launch. Each sampling kit was sent to the ISS onboard the SpaceX-5, -6, -8, rockets and returned to the Earth onboard the Russian vehicle (Soyuz TM-14) and Dragon capsule (SpX-6 or -8). Eight different locations were sampled on the ISS using the polyester wipes described above (see Fig. 1 for a summary of the sampling locations). The metadata associated with the samples and collections is summarized in Additional file 6 : Table S3.
The study requirements stated that there should be no cleaning at least 4 days prior to sampling. When the cleaning occurred during the weekends, it was done at the crew’s discretion without suggestions about the specific locations, therefore following the typical routine of activities on the ISS. The disinfectant wipes that are used in the ISS contain octyl decyl dimethyl ammonium chloride (0.0399%), dioctyl dimethyl ammonium chloride (0.01995%), didecyl dimethyl ammonium chloride (0.01995%), alkyl (50% C14, 40% C12, 10% C16) dimethylbenzylammonium chloride, and dimethylbenzylammonium chloride (0.0532%). During each flight, one astronaut performed all the sampling and used the wipes to sample one square meter. A new pair of individually packed sterile gloves (KIMTEC Pure G3 White; Nitrile Clean-room Certified; Cat. HC61190) were used before sampling the next location. The crew was instructed to collect samples from the same surfaces during all three sampling sessions. A control wipe (environmental control) was taken out from the Zip lock bag, unfolded, waved for 30 s, and packed back inside a new sterile zip lock. One control wipe was included for each flight session. Similarly, an unused wipe that was flown to the ISS and brought back to Earth along with the samples served as a negative control for sterility testing. If field controls (wipes that were exposed to the ISS environment but not used in active sampling) showed any signs of microbial growth, then negative controls would be assayed for cultivable counts to check sterility of the wipes used for sampling. However, none of the field controls showed any CFUs for all three flights. The samples were stored at room temperature in orbit. After sample collection, samples were returned to Earth after 7 days for Flight 1, 9 days for Flight 2, and 6 days for Flight 3. The kits were delivered to JPL immediately after arrival to Earth at 4 °C with processing at JPL commencing within 2 h of receipt.
The study requirements stated that there should be no cleaning at least 4 days prior to sampling. When the cleaning occurred during the weekends, it was done at the crew’s discretion without suggestions about the specific locations, therefore following the typical routine of activities on the ISS. The disinfectant wipes that are used in the ISS contain octyl decyl dimethyl ammonium chloride (0.0399%), dioctyl dimethyl ammonium chloride (0.01995%), didecyl dimethyl ammonium chloride (0.01995%), alkyl (50% C14, 40% C12, 10% C16) dimethylbenzylammonium chloride, and dimethylbenzylammonium chloride (0.0532%). During each flight, one astronaut performed all the sampling and used the wipes to sample one square meter. A new pair of individually packed sterile gloves (KIMTEC Pure G3 White; Nitrile Clean-room Certified; Cat. HC61190) were used before sampling the next location. The crew was instructed to collect samples from the same surfaces during all three sampling sessions. A control wipe (environmental control) was taken out from the Zip lock bag, unfolded, waved for 30 s, and packed back inside a new sterile zip lock. One control wipe was included for each flight session. Similarly, an unused wipe that was flown to the ISS and brought back to Earth along with the samples served as a negative control for sterility testing. If field controls (wipes that were exposed to the ISS environment but not used in active sampling) showed any signs of microbial growth, then negative controls would be assayed for cultivable counts to check sterility of the wipes used for sampling. However, none of the field controls showed any CFUs for all three flights. The samples were stored at room temperature in orbit. After sample collection, samples were returned to Earth after 7 days for Flight 1, 9 days for Flight 2, and 6 days for Flight 3. The kits were delivered to JPL immediately after arrival to Earth at 4 °C with processing at JPL commencing within 2 h of receipt.
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