Bacterial endospore inactivation caused by outgassing of vapourous hydrogen peroxide from polymethyl methacrylate (Plexiglas

Aims:  To investigate the cause and to eliminate the inactivation of Bacillus anthracis strain Sterne spores settled onto agar and stainless steel surfaces in plastic holders. Methods and Results:  In an experimental chamber in which spores settled onto sampling surfaces, vapourous hydrogen peroxide (VHP) was used for decontamination between experiments. It was demonstrated that hydrogen peroxide (H2O2) absorbed into plastic (Plexiglas®) surfaces and could outgas in the sample holders. Further experiments demonstrated that H2O2 was released from Plexiglas® sample holders in sufficient quantity to inactivate spores. High temperature degassing (30–35°C) for several days or aluminum coating of the surfaces were two remedies found to be effective in preventing inadvertent spore inactivation. Conclusions:  H2O2 can be absorbed into plastic and released after an extended period of time (weeks), allowing a sufficient concentration to accumulate in small volumes to inactivate spores. Outgassing the plastic or coating the surface with an impermeable layer are potential solutions to reduce spore inactivation. Significance and Impact of the Study:  Many studies with bacilli and other organisms are carried out using small plastic containers that may have been sterilized using H2O2 or other agents. This study presents a cautionary note to ensure elimination of H2O2 or other sterilizing agents to prevent spurious results.