Recovery of Bacillus Spore Contaminants from Rough Surfaces: a\ud Challenge to Space Mission Cleanliness Control

摘要

Microbial contaminants on spacecraft can threaten the scientific integrity of space missions due to probableinterference with life detection experiments. Therefore, space agencies measure the cultivable spore load(“bioburden”) of a spacecraft. A recent study has reported an insufficient recovery of Bacillus atrophaeus sporesfrom Vectran fabric, a typical spacecraft airbag material (A. Probst, R. Facius, R. Wirth, and C. Moissl-Eichinger, Appl. Environ. Microbiol. 76:5148-5158, 2010). Here, 10 different sampling methods were comparedfor B. atrophaeus spore recovery from this rough textile, revealing significantly different efficiencies (0.5 to15.4%). The most efficient method, based on the wipe-rinse technique (foam-spatula protocol; 13.2% efficiency),was then compared to the current European Space Agency (ESA) standard wipe assay in sampling fourdifferent kinds of spacecraft-related surfaces. Results indicate that the novel protocol out-performed thestandard method with an average efficiency of 41.1% compared to 13.9% for the standard method. Additionalexperiments were performed by sampling Vectran fabric seeded with seven different spore concentrations andfive different Bacillus species (B. atrophaeus, B. anthracis Sterne, B. megaterium, B. thuringiensis, and B. safensis).Among these, B. atrophaeus spores were recovered with the highest (13.2%) efficiency and B. anthracis Sternespores were recovered with the lowest (0.3%) efficiency. Different inoculation methods of seeding spores on testsurfaces (spotting and aerosolization) resulted in different spore recovery efficiencies. The results of this studyprovide a step forward in understanding the spore distribution on and recovery from rough surfaces. Theresults presented will contribute relevant knowledge to the fields of astrobiology and B. anthracis research.