Introduction:
Definition: Sterilization is defined as complete removal of microorganisms from an object, surface or a product.
It is essential that the process of sterilization must have strict control to ensure absence of viable organisms in the sterile products.
There are basically two types of controls,
Control on the process of sterilization i.e. Sterility Indicators or Sterility Monitors.
Sterility testing of the products.
Monitoring of sterilization can be done by employing either of,
Physical Indicator
Chemical Indicator,
Biological Indicator, for the sterilization process employed.
Physical Indicators:
Moist Heat:
A main “Master Process Record (MPR)” is prepared for a particular autoclave and for each specified product and load configuration.
This is then used as a reference for “Batch Process Record (BPR).
Nowadays sterilization cycles are controlled by microprocessors and pressure is measured through gauges or transducers.
Dry Heat:
A Master temperature record is prepared for a particular equipment which can be used as reference for each batch temperature setting.
Radio Sterilization:
Sterilization by radiation can be monitored by use of plastic dosimeters which can detect amount of dose absorbed during the process.
Gaseous Methods:
For gaseous sterilization process following steps are monitored,
Elevated temperatures during the sterilization cycle are recorded by “Temperature Probes”.
Gas leakage tests are done to ensure “Gas-tight” seals.
Gas concentration, weight of gas under pressure, humidity are measured and recorded.
Filtration Methods:
Bubble Point pressure test is conducted immediately after the process which ensures the integrity and determines the pore size of the filter in use.
Bubble Point pressure test:
Filter is soaked in an appropriate fluid and then the pressure is applied.
The pressure difference at which the first bubble of air breaks away is equivalent to maximum pore size of the filter.
On further increase of air pressure causes eruption of air bubbles all over the surface of filter, the air pressure is equivalent to mean pore size.
2) Chemical Indicators:
Chemical monitoring of the sterilization process involves change in chemical or physical properties of the chemical monitors by sterilization process.
The most common used chemical monitors are as follows,
Brown’s Tubes
Witness Tubes
Heat Sensitive Tape.
Royce Sachet
Chemical Dosimeters.
Brown’s Tubes:
Commonly used for heat processes.
These are small tubes containing reaction mixture and an indicator.
Exposure to high temperature causes a color change in the tube from red, yellow, brown to green showing a specific temperature.
Witness Tubes:
These tubes contain a substance of known melting point at a specific temp. e.g. Sulphur (115°C), Benzoic Acid (121°C) etc.
Melting of the substances indicates a specific temp. Achieved in the heat process.
Sometimes a dye like methylene blue is added for clear indication of melting.
Heat Sensitive Tape:
It is an adhesive tape used in autoclaving to indicate a specific temperature.
Autoclave tape works by changing color after exposure to temperatures commonly used in sterilization processes, typically 121°C in a steam autoclave.
Small strips of the tape are applied to the items before they are placed into the autoclave.
The tape is similar to masking tape but slightly more adhesive, to allow it to adhere under the hot, moist conditions of the autoclave.
One such tape has diagonal markings containing an ink which changes colour (usually beige to black) upon heating.
Royce Sachet:
It's a chemical indicator used for “Ethylene Oxide Sterilization”.
Its a polyethylene sachet containing magnesium chloride and bromophenol blue indicator.
Ethylene oxide penetrates polyethylene bags and reacts with the contents of the sachet.
At a given concentration - time exposure the color of the mixture changes from yellow to purple due to formation of “Ethylene chlorohydrin”.
Chemical Dosimeter:
It is the best technique available to measure radiation dose absorbed during sterilization by radiation.
The radio sensitive materials are impregnated in a plastic container and changes color from yellow to red on exposure to the radiations.
3) Biological Indicators.
It consists of a suitable microorganism deposited on a carrier and placed in load.
After sterilization they are collected and checked for viable microorganisms indiacating effectiveness of the sterilization process.
The microorganism to be used should possess following abilities,
Highly resistant to the sterilizing agent to be used.
Genetically stable.
Non pathogenic.
The viability of the organisms, storage condition, incubation and culture conditions must be standardized before the use.
The organisms usually used are spores as they are tougher life forms.
Most common biological indicators and sterilization processes are as follows,
Commonly asked Questions:
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