Mary E. Hummerick

Microbiological analysis of Lada Vegetable Production Units (VPU) to define critical control points and procedures to ensure the safety of space grown vegetables

The Lada Vegetable Production Unit (VPU), flight hardware currently deployed on the Russian module of the Internationl Space Station (ISS), is being used to validate the food safety of fresh “space-grown” crops. The goal is to develop a hazard analysis and critical control point (HACCP) plan to minimize potential microbial risks to the astronauts. Microbiological data has been collected from both plant tissue and hardware (e.g., root modules) returned from studies with a variety of crops grown on ISS. These data, which include estimates of microbial density and identification of the bacteria and fungi isolated, are useful in understanding and defining microbiological risks present in the ISS. In addition to flight studies, ground experiments have been done to define normal microbial loads and understand the fate and survival of human associated pathogens (Staphylococcus aureus, Salmonella enterica serovar typhimurium) in the Lada VPU. As part of the study, protocols were tested to determine the effectiveness of a sanitizer approved by the FDA and USDA (Pro-San) to achieve acceptable levels of microbes on VPU surfaces and vegetables. The sanitizer was used to clean chamber surfaces at regular intervals during four successive crop harvests, and as a post-harvest treatment of edible plant materials (i.e., mizuna leaves, radish bulbs). The sanitation protocol was effective in keeping the microbial density lower on the surfaces of the leaf chamber and root module and in reducing the numbers of culturable bacteria and fungi on the vegetables. These data have been used to develop a draft HACCP plan for space grown crops, which will be finalized during the next year.

Characterization of Volume F trash from four recent STS missions: weights, categorization, water content

accounted for 50% of the total trash and 69% of the total water for the four missions; drink items were 16% of total weight and 16% water; food wastes were 22% of total weight and 15% of the water; office waste and plastic film were 2% and 11% of the total waste and did not contain any water. The results can be used by NASA to determine requirements and criteria for Waste Management Systems on future missions.

VEG-01: Veggie Hardware Validation Testing on the International Space Station

Abstract The Veggie vegetable production system was launched to the International Space Station with three sets of test plants for an initial hardware validation test, designated VEG-01. VEG-01A and B featured the crop ‘Outredgeous’ red romaine lettuce, while VEG-01C tested ‘Profusion’ zinnia plants for longer duration growth and flowering characteristics. Irrigation of plants in all three growth studies presented a challenge, with lettuce suffering from inadequate water and zinnia suffering from excess water. Direct plant pillow watering by crew members enabled plant growth, and returned samples from the first crop, VEG-01A, indicated that food safety was acceptable. VEG-01B plants at harvest were split to allow for on-orbit crew consumption as well as science sample return. Direct-watered zinnias suffered fungal growth and other physiological stresses, but two plants survived and these produced numerous flowers. The VEG-01 series allowed a large amount of data on system performance, human factors, procedures, microbiology, and chemistry of space-grown plants to be gathered. Observations from these tests are helping to drive future hardware modifications and provide information on food crop growth and development in a microgravity environment.

Characterization of Volume F trash from the three FY11 STS missions: Trash weights and categorization and microbial characterization

This research project provided microbial characterization support to the Waste Management Systems (WMS) element of NASA’s Life Support and Habitation Systems (LSHS) program. Conventional microbiological methods were used to detect and enumerate microorganisms in space-generated solid wastes, i.e., STS Volume F Compartment trash returned from orbit and missions to ISS. Crew generated STS trash was characterized for three shuttle missions: STS 133, STS 134, and STS 135. The waste was catalogued into logical categories, weighed, and the water content determined. Results for FY11 STS missions showed more variability than for the FY10 study of STS 129-132 and indicated some waste was probably not included in what was returned to KSC on the STS. Microbial characterization of wastes from each mission and each category determined the presence of high numbers of microbes in food waste and food packaging, in drink pouches, and in personal hygiene wastes. A number of bacteria and fungi were identified, including known pathogens and some likely opportunistic pathogens that could cause problems if these wastes were exposed to an immune compromised crew.

Microbial Characterization of Space Solid Wastes Treated with a Heat Melt Compactor

The purpose of the project has been to characterize and determine the fate of microorganisms in space-generated solid wastes before and after processing by candidate solid waste processing. For FY11, the Heat Melt Compactor (HMC) was the candidate technology that was assessed. Five HMC product disks were produced at ARC from either simulated space-generated trash or from actual space trash. The actual space trash was the STS 130 Volume F compartment wet waste. Conventional microbiological methods were used to detect and enumerate microorganisms in heat melt compaction (HMC) product disks and in surface swab samples of the HMC hardware before and after operation. In addition, biological indicators were added to the STS trash prior to compaction to determine if these spore-forming bacteria could survive the HMC processing conditions, i.e., high temperature (160 ϒC) over a long duration (3 hrs). The HMC disk surfaces were sanitized with 70% alcohol prior to obtaining the core saples to ensure that surface dwelling microbes did not contaminate the HMC product disk interior. Microbiological assays were run before and after sanitization and found that sanitization greatly reduced, but did not eliminate, the number of identified isolates. To characterize the interior of the disks, ten 1.25 cm diameter core samples were aseptically obtained from each disk. These were run through the microbial characterization analyses. Low counts of bacteria, on the order of 5 to 50 viable cells per core, were found, indicating that the HMC operating conditions might not be sufficient for absolute sterilization of the waste. However, the direct counts were 6 to 8 orders of magnitude greater, demonstrating that the vast majority of microbes present in the wastes were dead or non-cultivable. An additional indication that the HMC processing conditons were sterilizing the wastes were results from commercial spore test strips that had been added to the wastes prior to HMC operation. Nearly all could be recovered from the HMC disks post-operation and all were showed negative growth when run through the manufacturer’s protocol, meaning that the 1 x 10 6 or so spores impregnated into the strips were dead. Control test strips, i.e., not exposed to the HMC conditions, were all strongly positive. One area of concern is that the identities of isolates from the cultivable counts included several human pathogens, namely Staphylococcus aureus.