Evaluating Quantitative Measures of Microbial Contamination from China's Spacecraft Materials

Different methods are used for the quantification of microbial load on spacecrafts. Here, we investigated a number of methodologies currently in use with the intent to identify the most accurate methods for the quantification of microbes on low-biomass metal surfaces such as those used in China's Space Station. In a previous study, we observed a high abundance of Bacillus sp. TJ 1-1 on interior surfaces of China's Space Station, and we therefore undertook this study in which we used a range of 10to 109 cells/100 cmof this strain for setting different contamination levels. Four of the most common analytical approaches (contact plate, spread plate, quantitative PCR, and BacLight™) were used to quantify the number of viable microbial cells associated with the materials of China's Space Station. Results show that, for 10cells/100 cm2, the contact plate method is the most convenient and reliable. For microbial contamination levels ≥10cells/100 cmand a sampling area of 121 cm2, the BacLight method proved to be most reliable for the detection of live cells. Moreover, a sampling area of 121 cmwas found to be the most suitable for analysis of metal surfaces for space station interiors, which are usually low in biomass. These results establish suitable sampling and processing methodologies for microbial enumeration of metal surfaces on China's Space Station.