Sterilization is a process of rendering an object or articles or substance free from all viable microorganisms, (bacteria , fungi , virus) here term viable is used because there might not be a living organism present after sterilization but its spores might germinate and give raise to microbial growth.
There are following method used for sterilization:
A) Heat Sterilization:
B) Chemical sterilization
C) Use of radiation
D) Ultra filtration
E) High Pressure.
Modes of action in sterilization process:
A) Heat Sterilization:
This includes. Following.
1) Dry heat sterilization.(Heating in high temperature oven)
2) Moist heat sterilization.( Autoclave)
3) Boiling in water
Dry heat causes coagulation and incineration of essential proteins and enzymes and breakdown bacterial cell wall, essential enzymes which are required for microbial growth are destroyed and prevents further growth of microorganism.
Some spores of bacteria and fungi can withstand higher temperature and upon on favorable conditions are attained they germinate in to microorganism. Hence a higher temperature and exposure time is longer in case of dry heat sterilization condition; many prefer 160 Degree Celsius for two hours, 170 Degree Celsius for one hour.
In dry heat sterilization hot air is heated up to required temperature and forced to circulate around article being sterilized. In this method objects are placed in SS trays over movable metal trolleys and these trolleys are placed in dry heat oven. After exposure for required time and temperature, these sterilizers (heat ovens) are opened from other side from inside of the processing room, and objects are unloaded directly in to microbiologically controlled environment or clean room.
Moist heat sterilization:
In this process object being sterilized is subjected to hot air saturated with steam, hot air with v vapour penetrate deep inside the article and bring about coagulation, denaturation, hydrolysis of cell wall proteins, microbial enzymes, this process is very effective as compared to dry heat sterilization as both heat and moisture at high temperature is very effective in destroying microorganisms.
An autoclave is sued for this process where in higher pressure inside the autoclave help in penetration of steam in to covered articles and time required in this process is less.
Temperature condition for Autoclave : 121°C for 30 minute at 15 psi pressure.
Chemical sterilization :
In method chemicals are used to achieve sterilization of surfaces and articles
Following are the chemicals used for chemical sterilization : Ethylene oxide , Nitrogen dioxide , Ozone, formaldehyde, Hydrogen peroxide, Peracetic acid, Silver, Iodine solutions.
Mode of action of chemical sterilization:
Most of the chemical bring about destruction of bacterial cell wall protein and enzymes.
Ethylene oxide : Its is very reactive in presence of moisture it ethylate DNA and RNA and enyme proteins. This causes destruction of bacterial cell.
Hydrogen Peroxide : It liberates free oxygen radical which oxidizes bacterial protein and essential enzymes.
Sterilization by filtration:
This method of sterilization is used for solutions, for injectable dosage form which cannot be heated and are thermolabile. Membrane filters made of mixester cellulose or polyethersulfone are used to filter solutions required to be made sterile. Inline glass filters of 0.2 µm are used for sterile filtration.
Filters of pore size less than 0.2 µm are capable of removing bacterial cells.
Filters of pore size 20 -50 nm are capable of removing viral cells this is called as nanofiltration.
Radiation : Radiation sterilization is used for articles which cannot be heated or treated with chemicals , Gama Ray Sterilization method is used for sterilization of articles packaged in a plastic moisture and air tight containers and exposed to gama radiation.