Biological Indicators are the test systems containing viable microorganisms providing a defined resistance to a specific sterilization process. A biological indicator provides information on whether necessary conditions were met to kill a specified number of microorganisms for a given sterilization process, providing a level of confidence in the process. Endo Spores or bacterial Spores are the microorganisms primarily used in Biological Indicators. They are considered some of the toughest ones to kill. Additionally, bacterial spores are chosen for a specific sterilization process based on their known resistance to that process. For example, Geobacillus stearo the rmophilus spores demonstrate a high resistance towards steam and vaporized hydrogen peroxide and are therefore used in BIs that monitor these sterilization processes.