Different Types of Sterilization

Sterilization :

·         Sterilization is a method  that can remove, kill and deactivate microorganisms.

·         Sterilization process eliminates (removes) or kills (deactivates) all forms of life and other biological   agents.

·         Sterilization can be achieved with one or more of the following

1.       Heat Sterilization

2.       Chemical sterilization

3.       Sterilization by radiation

4.       Gas sterilization done by ethylene oxide sterilization

5.       Filtration.

·         Depending upon the requirement these sterilization methods have different applications.

·         For example we can’t use dry heat sterilization 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 main concern is sterilization by moist heat and depyrogenation by dry heat.

     1.       Heat Sterilization:

·         Heat sterilization also Different types.

A.      Moist heat sterilization (Ex: autoclave)

B.      Other heat sterilization (Ex: Bunsen burner)

C.      Dry Heat sterilization (Ex: Dry heat sterilizer (DHS), Oven)

A.            Moist heat sterilization:

·         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 glassware, garments, rubber stoppers and    miscellaneous are sterilized at 121° Temperature and 15 PSI Pressure.

·         Pure steam is used for moist heat sterilization.

B.             Other heat Sterilization:

·         Flaming is done to loops and straight-wires in microbiology laboratory.

·         Leaving the loop in the flame of a Bunsen burner or alcohol lamp unit it glows red ensures that any infectious agent gets inactivated.

·         This method commonly used for small metals or glass objects, but not for large objects.

C.         Dry Heat Sterilization:

·         Depyrogenation by dry heat sterilization 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 increase the body temperature and can be very fetal.

·         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 250⁰C or 350⁰C is required and it depends upon the validation study.

     2.      Chemical Sterilization:

·         Chemicals are also used for sterilization.

·         But it is not always appropriate if it will damage heat-sensitive materials such as biological materials, fiber optics, electronics and many plastics.

·         Example :

1.       Isopropyl alcohol.

2.       Sodium hypochlorite (bleach) NaOCl

3.       Chlorine dioxide (ClO₂)

4.       Peracetic acid

    3.       Sterilization by radiation :

·         Sterilization can be achieved using electromagnetic radiation such as electron beams, X-rays, gamma rays, or irradiation by subatomic particles.

·         Electromagnetic or particulate radiation can be energetic enough to ionize atoms or molecules(Ionizing radiation), or less energetic (Non- ionizing radiation).

A.            Ionizing –Radiation sterilization.

B.            Non-Ionizing radiation sterilization.

    A.      Ionizing –Radiation sterilization:

·         Gamma radiation is very penetrating method.

·         This method is commonly used for sterilization of disposable medical equipment such as syringes, needles and food items.

·         It is emitted by a radioisotope, usually Coblat-60 (⁶⁰ Co) or cesium (¹³⁷ Cs).

·         Produced to speed light to kill the bacteria. Similar to light but higher photon energy and shorter wave length (electro magnetic quantum waves).

·         This process break down the microbial DNA.

·         Organisms there survive the process nonviable or unable.

·         Inhibiting the bacterial division.

·         25 kGy (kilo gray) of gamma irradiation has been recommended for terminal sterilization of medical products.

   B.      Non-Ionizing radiation sterilization:

·         Ultraviolet germicidal irradiation(UVGI) from a germicidal lamp is useful for sterilization of surfaces and some transparent objects.

·         Weave length  253.7 nm or 2537 Angstroms.

·         This weave length break down the microorganism DNA.

   4.       Gas Sterilization done by Ethylene Oxide :

·         Ethylene oxide (EO or EtO)  formula C₂H₄0.

·         Is a flammable colorless gas.

·         3% Eo gas mixed to air and pass. Most of the time it is mixed with nitrogen or Co₂ gas.

·         Sterilize time around at 60 hrs.

·         This method suitable for plastic, electro devices.

    5.       Filtration:

·         Filtration allows for the exclusion of organisms based upon size.

·         There are many types of filtration techniques (ex: membrane filters, catrdage filters---etc) but when sterilizing a system membrane filtration is used.

·         Membrane filtration traps contaminants larger than the pore size on the surface of the membrane.

·         If contaminants are smaller than the desired particle, decrease the membrane pore size and trap the product while passing the contaminants through the membrane.

Sterility and Bacterial endotoxin test (BET) are two important tests for the release of any injectable products. By sterility test we can able to detect the contamination in living from if present. If microorganisms are present in dead from then sterility test is not able to detect the contamination.

BET is another critical test and by this testing 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 gram negative bacteria. That’s why both 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 endotoxin are very stable (resistive) for sterilization by moist heat at 121⁰C  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 clear, if  we want to kill the live microorganism contamination sterilization by moist heat sterilization is effective and if we want to remove endotoxin ( produced by dead gram negative bacteria) then depyrogenation is required.