There are specific NASA requirementsfor source-specific encapsulated microbial density for encapsulated organisms in non-metallic materials. Projects such as the Mars Science Laboratory (MSL) that use large volumes of non-metallic materials of planetary protection concern pose a challenge to their bioburden budget. An optimized and adapted destructive hardware technology employing a commercial blender was developed to assess the embedded bioburden of thermal paint for the MSL project.
The main objective of this optimization was to blend the painted foil pieces in the smallest sizes possible without excessive heating. The small size increased the surface area of the paint and enabled the release of the maximum number of encapsulated microbes. During a trial run, a piece of foil was placed into a blender for 10 minutes. The outside of the blender was very hot to the touch. Thus, the grinding was reduced to five 2-minute periods with 2-minute cooling periods between cycles. However, almost 20% of the foil fraction was larger (>2 mm). Thus, the largest fractions were then put into the blender and reground, resulting in a 71% increase in particles less than 1 mm in size, and a 76% decrease in particles greater than 2 mm in size.
Because a repeatable process had been developed, a painted sample was processed with over 80% of the particles being <2 mm. It was not perceived that the properties (i.e. weight and rubber-like nature) of the painted/foil pieces would allow for a finer size distribution. With these constraints, each section would be ground for a total of 10 minutes with five cycles of a 2-minute pulse followed by a 2- minute pause. It was observed on several occasions that a larger blade affected the recovery of seeded spores by approximately half an order of magnitude.
In the standard approach, each piece of painted foil was aseptically removed from the bag and placed onto a sterile tray where they were sized, cut, and cleaned. Each section was then weighed and placed into a sterile Waring Laboratory Blender. Samples were processed on low speed. The ground-up samples were then transferred to a 500-mL bottle using a sterile 1-in. (≈2.5-cm) trim brush. To each of the bottles sterile planetary protection rinse solution was added and a modified NASA Standard Assay (NASA HBK 6022) was performed. Both vegetative and spore plates were analyzed.
This work was done by James N. Benardini, Robert C. Koukol, Gayane A. Kazarians, Wayne W. Schubert, and Fabian Morales of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48302
This Brief includes a Technical Support Package (TSP).
Using a Blender to Assess the Microbial Density of Encapsulated Organisms
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Overview
The document titled "Using a Blender to Assess the Microbial Density of Encapsulated Organisms" is a technical support package from NASA's Jet Propulsion Laboratory (JPL) that outlines a method for evaluating microbial density in encapsulated organisms, particularly in the context of ensuring sterility in medical device manufacturing. This work is part of NASA's broader efforts to adhere to planetary protection provisions for robotic extraterrestrial missions, as outlined in NASA Procedural Requirement 8020.12C.
The document details the development of a destructive hardware technology that utilizes a commercial blender to assess the microbial embedded bioburden in thermal paint used on the Mars Science Laboratory (MSL) project. The encapsulated microbial density in nonmetallic materials is specified to range from 1 to 30 spores/cm³, which is relevant for the thermal paint applied to the MSL.
The methodology involves several steps, starting with the grinding of painted aluminum foil samples. The samples are first weighed and then ground in a sterile laboratory blender for a specified duration, followed by sieving to determine the size fractions of the ground material. The ground samples are then processed with a sterile rinse solution, and a modified NASA Standard Assay is performed to quantify the microbial content. Both vegetative and spore plates are incubated and counted at various intervals to assess recovery percentages of Bacillus atrophaeus spores, which serve as a positive control.
The document emphasizes the importance of using appropriate controls, including negative controls with sterile aluminum foil and positive controls with known quantities of spores, to validate the efficacy of the assay. The results from these assays are crucial for ensuring that the painted aluminum foil used in space missions does not harbor harmful microbial life, thereby protecting planetary environments.
Overall, this technical support package not only highlights the innovative methods developed for microbial assessment but also underscores the significance of maintaining sterility in aerospace applications and medical device manufacturing. The research conducted by the team at JPL reflects a commitment to scientific rigor and compliance with safety standards, contributing to the broader goals of NASA's exploration missions.
