Freezing: Inactivation of living bacteria by cold. It prevents active multiplication of bacteria by decreasing the metabolic activity of bacteria. Lyophilization : Freeze-drying : Involves rapid freezing with subsequent drying.
Use: . Preservation of microbial cultures. . Preservation of vaccines.
f. Filtration : Mechanical sieving through membrane filters. Uses: . Sterilization of thermolabile parental and ophthalmic solutions, sera and plasma. . Microbial evaluation of water purity. . Viable counting procedures. . Determination of viral particle size
Radiation : Ioning and ultra violet radiation Ioning radiation includes χ ray, γ ray and β ray. These induce break down of single stranded or sometimes double stranded DNA. Ultra violet radiation has less quantum energy with low penetrating power than ionic radiation. Spore forming bacteria are more resistant to ionic and ultra violet radiation than vegetative bacteria because of:
The spore coat confers protection.
DNA is in different state in spores. 103