Sterilization is the killing or removal of micro-organisms and their spores from the substance, material, or Preparation required to be used in sterile form or Sterilization is the process by which an object’s surface as a medium becomes free from all harmful microorganisms both in the vegetative and sporing stage are sterilized by removing or killing them.
Method of Sterilization Microbiology:
1) Physical Methods :
a) Dry Heat Sterilization
b) Moist Heat Sterilization.
c) Radiation Sterilization. (UV and Gamma radiations.)
2) Chemical Methods :
a) Ethylene Oxide Gaseous Sterilization
b) Use of Antimicrobial Agents.
3) Mechanical Method :
a) Filtration through Bacteria Proof Filter.
Different types of Sterilization Process:
1) Physical Methods:
a) Dry Heat Sterilization (DHS): It is suitable for heat-stable, non-aqueous products and powders, ampoules and vials, and glassware’s sterilization and depyrogenation. The time and temperature cycle are as follows:
180°C temp. for 30 min.
170°C temp. for 1 hour.
160°C temp. for 2 hours.
Glass Depyrogenation can be done at 250°C temp. for 2 to 3 hours. According to IP 2007 sterilization techniques, the reference condition should be at a minimum of 160°C for 2 hours; other time and temperature combinations may be used provided that it has been satisfactorily demonstrated that the process chosen delivers an adequate level of lethality when operated routinely within the established tolerance.
The precautions and practices used should be such that a SAL of 10-6 or better is obtained. An acceptable range in temp. in the empty chamber is ± 15°C, when the unit is operating at not less than 250°C. A SAL (Sterility Assurance Level) of 10-12 is considered achievable for heat-stable articles or components.
Mode of action: Bacterial Cell Protein Oxidation.
b) Moist or Steam Sterilization (autoclave): This involves heating in an autoclave with saturated steam under pressure and it is applicable for Aqueous preparations and Surgical material. Time and Temperature cycle :
|Holding Temp. (°C)
|Minimum Holding Time (Minutes)
|115 to 118°C
|121 to 124°C in case of an aqueous preparation
|126 to 129°C
|134 to 138°C
As per the Indian pharmacopeias reference condition for steam sterilization, Aqueous preparations are heated at a minimum of 121°C for 15 minutes. Other timings and temperature combinations are acceptable as long as it has been sufficiently proven that the procedure chosen produces an adequate level of lethality when applied regularly within the defined tolerance.
The precautions and practices used should be such that a SAL of 10-6 or better is obtained. F0 concept may be used for establishing the sterilization cycles. When surgical materials are sterilized the steam used should neither be superheated nor contain 5 % of entrained moisture. Appropriate steps should be taken to ensure adequate removal of air. Most dressings are conveniently sterilized by maintaining a temperature of 134°C to 138°C for 3 minutes.
Mode of action: Precipitation of cell proteins of the bacterial cell wall.
c) Radiation Sterilization:
i) UV Radiations: The UV light of Wavelength 2537 Angstrom units is commonly employed for sterilization. The principle effect may be on cellular nucleic acids which have been shown to exhibit strong absorption bands within the UV wavelength range. Applicable for sterilization of Room, Air, Air ducts, Water and Linens, etc.
ii) Ionizing Radiation Sterilization of drug substances, dosage forms, and medical devices may be achieved by exposure in the final containers or packs to ionizing radiations in the form of gamma radiations from suitable radio isotopic sources such as Cobalt – 60 or Cesium 137. For gamma radiation sterilization, an effective sterilizing dose that is tolerated without damaging effect is about 25 kGY (2.5 Megarads) Ionizing Radiation destroys micro-organisms by stopping reproduction as a result of lethal mutation.
2) Chemical Method:
Ethylene Oxide Sterilization (ETO): This process involves exposure to a sterilizing gas. It is used for sterilization of plastic tubing, dressing, cardboards, and rubber gloves. The material to be sterilized is placed in the chamber and exposed to Relative Humidity up to 98 % for a period of 60 minutes or longer. It is then placed in a chamber previously heated to about 55°C and an initial vacuum of approximately 27 inches of Hg is drawn. Ethylene oxide is then introduced, along with moisture to achieve 50 to 60% RH. To the pressure required to give the desired concentration of ETO, which is maintained throughout the exposure period.
Mode of Action: Kills micro-organisms by alkylating essential metabolites, affecting particularly the reproductive system. The altered metabolites are not available to the micro-organism, and so it dies without reproduction.
3) Mechanical Method:
Filtration Methods: This method may be used for certain active ingredients and preparations that are not sufficiently stable to heat to allow sterilization by steam. The process depends on the physical removal of micro-organisms by adsorption on a filter medium of nominal pore size of 0.22-micron meter or less.
Purpose of Sterilization
- To render the object free from pathogens.
- To make complete removal or destruction of all forms of microorganisms.
- To sterilize all the processed equipment used inside the lab.
- To keep all the equipment ready for use.
Related Topics: Aseptic and Sterile in Pharmaceutical
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