<P> The aim of sterilization is the reduction of initially present microorganisms or other potential pathogens . The degree of sterilization is commonly expressed by multiples of the decimal reduction time, or D - value, denoting the time needed to reduce the initial number N 0 (\ displaystyle N_ (0)) to one tenth (10 − 1 (\ displaystyle 10 ^ (- 1))) of its original value . Then the number of microorganisms N (\ displaystyle N) after sterilization time t (\ displaystyle t) is given by: </P> <Dl> <Dd> N N 0 = 10 (− t D) (\ displaystyle (\ frac (N) (N_ (0))) = 10 ^ (\ left (- (\ frac (t) (D)) \ right))). </Dd> </Dl> <Dd> N N 0 = 10 (− t D) (\ displaystyle (\ frac (N) (N_ (0))) = 10 ^ (\ left (- (\ frac (t) (D)) \ right))). </Dd> <P> The D - value is a function of sterilization conditions and varies with the type of microorganism, temperature, water activity, pH etc...For steam sterilization (see below) typically the temperature (in ° Celsius) is given as index . </P>

Describe three other types of sterilization techniques that are used in the microbiology laboratory