Methods of sterilisation in microbiology

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Pharmaceutical microbiology assignment



Sterilization –a process that by which all viable M.O are removed or destroyed , based on a probability function .

Sterilization concept

Sterilization is essential concept in the preparation of sterile pharmaceutical products . its aim is to provide a product that is safe and eliminates the possibility of introducing




Moist heat sterilization

saturated steam autoclaves

superheated water autoclaves

air over steam autoclaves

Dry heat sterilization

Batch sterilizers

Continuous tunnel sterilizers

Moist –heat sterilization

ï‚-Microorganism are destroyed by cellular protein coagulation.

ï‚-The objects to be sterilized are exposed to saturated steam under 1 atmosphere pressure at a minimum temperature of 121°Cfor at least 20-60 minutes.

ï‚-An autoclaveis commonly used for moist –heat sterilization .

ï‚-Because it does not require as high a temperature, moist –heat sterilization cause less product and equipment damage compared to dry –heat sterilization .


Is a device to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121°C or more, typically for 15-20 minutes

Autoclaves types /

ï‚-Portable autoclave (bench autoclave)

ï‚-Stationary autoclave (large steriliser)

ï‚-For porous loads e.g., dressing

ï‚-For bottled fluids

Portable autoclave (bench autoclave)

Stationary autoclave (large sterilizer)

Main features of autoclaves

1.Lid(door) fitted with clamps and asbestos jacket , stationary autoclave may be double doors at both ends one for loading and one for unloading.

2- pressure gauge

3.Thermocouple for measurmentof temp. usually located withginthe discharge channel in dummy article.

4- air vent remove air before sterilization

5- safety valve to prevent the escape of excess steam causing explosion

.6. Modern autoclaves are recording (record pressure, temp during the whole process ) supplied

With timer ant automatically controlled .

Advantage of jacket autoclave

  1. Rapid in operation as steam stored in the jacket.
  2. More economic as steam trapped in the jacket not allowed to escape to the atmosphere
  3. Load comes out dry as the inner surface is always warm

Operation of the autoclave

1.Articles to be sterilized are placed in baskets or cylinders.

2.Door is closed and clamped

3.Heating is started and steam is generated

4.Air vent is closed after complete removal of air (noticed by continuosand vigorous flow of steam from the air vent .

5.When pressure reached that required 1 atm, 121 C , sterilization period is timed .

6. At the end of the period , heat is disconnected .

7. Autoclave should be not opened before pressure is fallen down.

Air must be removed from autoclave//*

ï‚-Because :

1.It reduces the penetration of steam especially with decreasing .

2.It cause superheating in stationary autoclaves.

3.In temp. controlled autoclaves explosion may occur.

There are many types of autoclave/// gravity displacement ,positive pressure displacement ,and negative pressure - vacuum- displacement:

  • The autoclave tattoo in the US is usually the type gravity displacement ofautoclaves , or calledtype "N". This type of autoclave in general depends on heating element compeletely or partially submerged in a pool of water at the bottom of the autoclave chamber , along with a hole that carry water from a reservoir to autoclave chamber. As the water in the pool is heated then begins to evaporate, forming the steam. Steam is lighter than air, when the chamber filled with steam the major amout of air in the chamber is pushed to bottom of the chamber, and escapes throughout the fill hole which is contact to a temperature sensitive diaphragm which stops when it is sufficiently heated. Once the diaphragm closes the pressure exerted inside the autoclave chamber. The benefit of this type of autoclave is its simplicity in use , the drawback with gravity displacement autoclaves is they are only designed to use properly with solid unwrapped instruments, but there has been no indication that a gravity displacement autoclave , properly loaded with properly processed instruments is unsafe for use in the modification industry.
  • Apositive pressure displacement autoclave developed on the design of a gravity displacement autoclave the modification is by creating the steam in a separate internal part, called the "steam generator". When the amount of steam needed to displace air in the chamber is produced a valve opens and a pressurized burst of steam enters the autoclave chamber, leads to higher percen of air from the chamber that removed then with a gravity displacement autoclave , this decreases th cycle times of autoclave. Now the most widely distributed in world and used if not being the only positive pressure displacement autoclave is the Statim line of autoclaves. The drawbacks to positive pressure displacement autoclaves are the high cost, and there is a fact that they in general have a smaller chamber.
  • Negative pressure, orcalled the vacuum displacementautoclaves, also known astype S, having separated internal "steam generator", in addition to a vacuum pump. After the autoclave chamber is closed the vacuum pump removes then all air form the chamber, and as above, steam is trapped into the chamber. Negative pressure displacement autoclaves are able to maintain kindly the higheststerility assurance levelor calledSAL. Negative displacement autoclaves in general have a filtered air drying system which allows the autoclave packages to be completely dries before having any ambint air. The drawback back to negative pressure displacement autoclaves is thier cost, and may be in sometimes the size of these systems also .
  • The last "type" of steam autoclave is calledtype "B"forthw word Big, and the name indicate itself. systems like those are more or less enlarged of negative pressure displacement autoclaves (there are enormous gravity displacement autoclaves as well, but still type "N", and not usually used in the medical or modification industries). The steam generator for Type "B" autoclaves is a separated stand alone part, and the autoclave chamber is sometimes large enough to physically enter. Due the large scale and astronomical price tag of these autoclaves they are rarely, if ever used in the modification industry.

List of references

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