Bacillus stearothermophilus Sterilization is generally defined as the process of completely destroying ble microorganisms including structures such as spores. Standandard practice in sterilization process is to include sterility indicator along with the aicles to be sterilized. The use of sterility indicators allows a direct and sensitive approach to test the effectiveness of the sterilization process. Sterility indicators can be biological or chemical. Biological indicators A biological indicator is broadly defined as a characteristic preparation of specific microorganism that provides a defined and stable ressitance to specific sterilization procedures. The biological indicators selected should provide a greater challenge to the sterilization process than the bioburden in or on the product. Microorganisms widely recognized as biological indicators are spore forming bacterias because these organisms are significantly more resistant than the normal. - With the exception of ionizing radiation process, these microorganisms are significantly more resistant than the normal micro flora. A biological indicator can be used to assist in the performance qualification of the sterilization equipment and in the development and establishment of a validated sterilization process for a paicular process. "Biological indicator used in plasma sterilization is Bacillus stearothermophilus". Plasma sterilization Plasma is described as the fouh state of matter (It is neither liquid, gas or solid). it is defined as reactive cloud of ionized atoms, electrons and neutral atomic paicles. In order to generate the plasma for sterilization, matter (for example H202) a gaseous state is exposed to strong electrical or magnetic .field. This is performed in a vaccum so that high temperature are not required. In practice, a hydrogen peroxide solution is dispersed in a vaccum chamber creating a plasma cloud. This result in the generation (ionisation) of a cloud of charged paicles and free radicals that interact with vital cell component. The free radicals generated during this process interacts with vital cell component (mainly nucleic acids and destroy them). Sterilization occurs as a result of the dual phase process of the oxidative propeies of the vapour and plasma. Gas plasma is capable of penetrating medical packaging, is safe to use and the sterilization cycles are easy to control and monitor. The temperature attained in these process is not very high so there is no risk of damage of the instruments as in Heat methods. Biological indicators for various sterilization methods B. stearothernzophilus spores are used to monitor -Steam sterilization - Plasma sterilization (hydrogen peroxide) - Liquid peracetic acid sterilizers