Quantitative determination of bacterial spore association with particles in cleanroom environment

In order to establish a creditable biological contamination transport model for predicting the cross contamination risk during spacecraft assembly and upon landing on Mars, it is important to determine the quantity and size distribution of bacterial spore containing particles on the surface of spacecraft in cleanroom. We conducted an extensive set of air and surface sampling in indoor, outdoor, and cleanroom environments and determined the ratios of the number of spore forming bacteria to that of their dust particle carriers of various sizes. We found that the average number of cultivable spore forming bacteria on particles of >; 7 microns is ~ 10^-2 while on particles of <; 1 microns ~ 10^-6. Our data also confirmed the existence of multiple spores on a single particle. The results from these studies are essential for developing a reliable biological contamination transport model for meeting the Planetary Protection requirements for future Mars Missions.