An observation about the relative hardiness of bacterial spores and planetary quarantine

Abstract

Currently, planetary quarantine spacecraft sterilization requirements are based on the ‘logarithmic’ model of bacterial death. This model is a single parameter exponential model in which the sole parameter is the decimal reduction time (D-value). The D-value associated with the sterilization of a population of bacteria is only a relative measure of the rate of bacterial inactivation: It is known to depend upon many factors, but generally these dependencies are not thoroughly understood. The D-values chosen for spacecraft sterilization have been selected conservatively relative to defined experimental procedures and bacterial spore stocks. New data indicate that these D-values are not conservative when compared with those of naturally occurring organisms. The possible implications of these new data for planetary quarantine are analyzed here.