Sterilization by dry heat and moist heat and its relation to BET (bacterial endotoxin test) and Sterility test

Hello Friends, 

                     By this blog I am going to discuss about the the process of Sterilization by moist heat and depyarogenation by dry heat and two major testing in microbiology for the release of any injectable product e.g Sterility and BET (Bacterial endotoxin testing).

There is some confusion about these two processes and testings, like some people ask me is there any requirement to perform both Sterility and BET for release of product? Can,t we perform either Sterility or BET? Another question people ask me most of the time that both these methods are used for sterilization so what is the requirement of sterilization by moist heat and sterilization by dry heat? The answer is here for this confusion.

Sterilization: Sterilization is a process by which we can get any article sterile. There are different methods of sterilization as mentioned below.

1. Moist heat sterilization by autoclaves
2. Dry heat sterilization by dry heat sterilizers/Ovens
3. Irradiation sterilization by gamma radiation  
4. Chemical sterilization by using chemicals
5. Gas sterilization done by ethylene oxide gas
6. Physical sterilization by membrane filtration

Depending upon the requirement these sterilization methods have different applications. For example we can't use dry heat method for sterilization of plastic material. These sterilization methods depend upon the nature of product to be sterilized. All these methods are used in pharmaceutical industries but my main concern is Sterilization by moist heat and depyarogenation by dry heat.

Sterilization by moist heat: Moist heat sterilization is one of the very effective method of sterilization for the items which we can't sterilize by dry heat. By using autoclaves different loads like glasswares, garments, rubber stoppers and miscellaneous are sterilized at 121 degree celcius temperature and 15 pascal pressure. Pure steam is used for moist heat sterilization.

Depyrogenation by dry heat: Depyrogenation by dry heat is a process by which we can get any article sterile as well as endotoxin free. Endotoxins are by products of gram negative bacteria which are released in to the blood stream after microbial cell death. Endotoxins can increase the body temperature and can be very fatal. This increase of body temperature in uncontrolled manner leads to death of the person. Dry heat sterilizers and ovens are used for this process of depyrogenation and high temperature like 350 degree celsius is required and it depends upon the validation study.

Sterility and  Bacterial endotoxin test are two important tests for the release of any injectable products. By sterility test we can able to detect the contamination in living form if present. If microbes are present in dead form then sterility test is not able to detect the contamination. BET is another critical test and by this testing (BET) we can only detect endotoxin which is release by dead gram negative bacterial cells. So, application of both these tests are different, one can detect live contamination and another can detect endotoxin produced by dead bacteria. That's why both these testing are must for release of any injectable product. Another thing is that we can't use moist heat sterilization method to remove/denature the endotoxin because endotoxins are very stable moiety and sterilization by moist heat at 121 degree celsius has no impact on the property of endotoxin. It means endotoxin can't be denatured by the process of moist heat sterilization that's why dry heat sterilization is required. Now it is now clear that if we want to kill the live microbial contamination sterilization by moist heat is effective and if we want to remove endotoxin produced by dead gram negative bacteria then depyrogenation is required.

Thanks and have a great day :)