A short discussion on comparing advantages and disadvantages of dry-heat and moist-heat sterilization.
What is dry heat sterilization ?
Dry-heat sterilization is generally a less complicated process than steam or moist-heat sterilization; it is however relatively slow and requires higher temperatures or longer exposure times.
What is moist heat sterilization ?
Whereas sterilization with steam under pressure, mainly at 121 degrees centigrade, 15 pounds of pressure for 20 min(pressure should be 1.2kg/cm) is known as moist-heat sterilization. Moist-heat sterilization is the steam sterilization in which temperature and pressures both works.
Now let’s see about the comparison of mechanisms and uses of the both sterilization process:
Mechanism of killing process by dry-heat sterilization:
l Dry-heat kills the organisms by destructive oxidation of essential cell constituents
l Killing of moist resistant spores by dry heat requires a temperature of about 160 degree centigrade.
l Dry-heat is employed for glassware; syringes, metal instruments and paper wrapped goods, which are not spoiled by high temperatures.
l It is also used for anhydrous fats, oils and powders that are impermeable to moisture.
Mechanism of killing process by moist-heat sterilization:
l Moist-heat kills the organisms by coagulation and denaturing their organisms and structural proteins.
l Sterilization by moist-heat of the moist heat resistant spores generally requires 121 degree centigrade for 15-30 minutes.
l Upon heat proteins release free –SH groups and form smaller peptide chains which in form next complexes different from the original protein molecules.
l Moist-heat is more effective than dry-heat.
l This process is used for the sterilization of culture media and all materials through which steam can penetrate.
l Moist-heat can be done at lower temperatures in given time at a shorter duration at the same pressure.
As both sterilization processes have different methods and used in different purpose, the advantage and disadvantage is a big factor in the process of sterilization. So we must have a proper knowledge on them.
Advantages of dry-heat sterilization:
l Reliable, non-toxic and effective method of sterilization of heat stable articles.
l Low cost and easy to install.
l As the instruments remains dry after sterilization, there are no chances of corrosion .
l This is the only method of sterilizing oils and powders.
Disadvantages of dry-heat sterilization:
l When Cotton wool and paper is used in this sterilization method, it may get slightly charred.
l Exposure to the higher temperature may be harmful to the instrument.
l Takes longer time compared to autoclave.
l Glasses may become smoky.
Advantages of Moist-heat sterilization:
l Requires low temperature:
l Less time to complete.
l Easy to control and monitor.
l Also low cost and non-toxic.
l Quicker than hot air oven.
Disadvantages of Moist-heat sterilization:
l The heat sensitive instruments cannot be sterilized.
l After sterilization, the instruments remain wet, which may lead to rust.
l Chances of getting instrument damaged, due to repeated exposure.
l Trapped air may reduce efficacy and takes long time to cool.
A short discussion on aseptic technique sterility test, its method and importance and interpretation results for the sterility test.
Sterility test is defined as the testing which confirms that products are free from the presence of viable microorganism such as virus, bacteria, spores etc. It is very important for medical devices, pharmaceuticals, preparations, tissue materials and other materials that are claiming to be free from viable microorganisms.
Methods:
There are two types of sterility testing method in general:
l Membrane-filtration method and
l Direct-inoculation method.
1. Membrane-filtration method:
Membrane filtration is the method of choice for the filterable pharmaceutical products. According to USP<71> in this sterility testing method products are flitted through 0.45 to 0.45 or 0.2 micron membrane filter.
Five basic steps are involved in the use of the Membrane-filtration method:
l The filter unit must be properly assemble and sterilized prior to use.
l The contents of the prescribed number of units are transferred to the filter assembly under strict aseptic conditions.
l The contents with the filtered with the aid of the vacuum or presence differential system.
l One half of the membrane is placed in suitable volume (usually 100ml) of FTM and their other membrane, half is placed in equal volume of TSB.
2. The Direct-inoculation method:
The direct-inoculation or direct-transfer method is the method of choice for the medical devices and non-filterable pharmaceutical products, which include solid dosage form, powders, ointments and creams.
Basically the method involved three steps:
A. Aseptically opening each sample container from recently sterilized batch of product.
B. Using a sterile syringe or needle to withdraw the required volume of sample for both media from the container.
C. Injecting the one half of the required volume of FTM and the other half volume of sample into a second test containing the required volume of TSB.
Now let’s Reed about what happens in the observation part, so we can realize the interpretation results of the sterility test:
At intervals, during the incubation period and its conclusion e.g. the media for microscopic evidence of microbial growth, if no evidence of growth is found, the preparation being examined passes the test for sterility. If evidence of microbial growth is found, the containers should be reserved, unless it can be demonstrated by any other means that their presence is due to unrelated to the preparation being examined and hence the test for the sterility, is invalid and may therefore be recommended, perform a retest. If no evidence of microbial growth is then found, the preparation being examined passes the test for sterility. If evidence of microbial growth is found, now the organisms should be isolated and identified. If no evidence of the microbial growth is found in the second retest, the preparation being examined passes the test for sterility. If evidence of microbial growth is found in the second retest, thus fails the test for sterility.
Aseptic technique:
Aseptic technique means using practices and procedures to prevent contamination from pathogens. It is designed to provide a barrier between the microorganisms in the environment and the sterile cell culture to reduce the probability of contamination from these sources. Health-care workers, use antiseptic technique in surgery-rooms, clinics, out patient-care settings. It is used in pharmaceutical industries also.
Aseptic technique is used in various purposes. Health-care professional commonly use aseptic technique when they are:
l Handling surgery equipment.
l Helping with a baby’s birth by vaginal delivery
l Handling dialysis catheters.
l Performing dialysis.
l Inserting a chest tube
l Inserting other draining devices.
l Performing various surgical techniques.
The elements of aseptic technique are a sterile work area, good personal-hygiene, sterile reagent sterile handing etc.
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