In any microbial study, it is crucial to ensure that media, glassware, and working surfaces are free from contaminants through sterilisation. This process can be achieved using physical and chemical methods. Physical methods include heat, radiation, and filtration, whereas chemical methods involve the use of specific chemical agents.

Sterilisation by heat is considered the most effective and rapid method for articles that can withstand heat. Heat acts by denaturation and coagulation of proteins, exerting oxidative effects, and interfering with metabolic reactions. One such method is boiling, where syringes, rubber goods, and surgical instruments are sterilised at 100°C for 30 minutes in a boiling water bath.

Another physical method is autoclaving, which uses steam at temperatures higher than 100°C under pressure; it is one of the most common methods in laboratories. Heating and flaming are dry heat methods where objects like inoculation loops are held in a flame until red hot, while test tube mouths are passed through the flame. A hot air oven is also used to sterilise glassware.

Sterilisation by chemicals involves agents like alcohols, aldehydes, and heavy metals. Alcohols such as 70% ethyl alcohol sterilise surfaces through cell dehydration and protein coagulation. Aldehydes like 40% formaldehyde (formalin) are used for fumigation. Heavy metals like mercury and silver act as germicides by precipitating proteins. Hydrogen peroxide is also used for skin disinfection.