Effect of bacterial cell moisture on the sporicidal activity of beta-propiolactone vapor.

The activity of a vapor-phase disinfectant is usually expressed in terms of the atmospheric relative humidity (RH). This study shows that, in beta-propiolactone (BPL) vapor disinfection, the important factor is really the moisture content and location of water in the cell, and not necessarily the atmospheric RH. Previous studies revealed that only about 50% of the bacterial spores equilibrated to 45% RH were killed when exposed to the same RH to BPL vapor. On the other hand, all the spores equilibrated to and then exposed at 75% RH to BPL were readily killed. The present study shows that spores equilibrated to 98% RH are readily killed by BPL at 45% RH, but only 99% of the spores equilibrated to 75% RH are killed by BPL at 45% RH. Also, in order to be killed, desiccated spores must be exposed to BPL at higher humidities than would be required if the spores had not been previously desiccated.