Principle Microbiology

Fractional sterilization : -
Some mocrobiological materials can not be heated above 100 degree C. But if still they can withstand the temperature of free flowing steam (i.e. 100 degree C) they can be sterilized by fractional sterilization / Tyndalization. In this method the material is heated with steam of 100 degree C on three successive days with incubation period in between. The vegetative cell will die on the 1st exposure with heat and the spores will germinate in incubation period. This germinated spores can be killed on second exposure with heat. If the spore will germinate it will become vegetative cell which can be easily destroyed, but if it doed not germinate sterilization will not be obtained. After three exposures sterilization is obtained. For this method one can use steam arnold. Even an autoclave with free flowing steam can be used for this purpose.