Sterilization techniques

Sterilization techniques

Sterilization:

Is the destruction or complete removal of all forms of microorganisms including the spores from any substances. This can be achieved by the following means:
1. Physical methods:
A- Heat:
Is the most applicable and reliable method of sterilization, should used where possible. It includes:
1. Moist heat: Involve heating in the presence of water. It can be classified into:
A. Pasteurization (temp. below 100?C): Disinfection by most heat below 100 celled pasteurization, this method does not destroy spores and it is carried out by temp. at (56-60?C for 30-60 min.), e.g. milk.
B. Boiling (temp. around 100?C): Heating in boiling water at (100?C for 5-10 min.), e.g. surgical instruments and other metal objects.
C. Autoclaving (temp. above 100?C): Provides moist heat at temp. above 100?C by exposing the load of saturated stem at pressure greater that atmospheric pressure. It is an excellent agent for sterilization and a reliable method for sterilizing culture media, lab. coats, surgical dressing and all materials that are water containing and not to be damaged by high temperature.
The optimum conditions of autoclaving are:
- 121?C for 15 min. at 15 psi (pound/inch2) (1.5 bw).
- 126 ?C for 10 min.
- 134 ?C for 3 min.
2. Dry heat: Include:
A. Flaming (Incineration): Red heat has its main application in the sterilization of inoculating wires, loops and forceps which should be held vertically in a Bunsen burner flame until got red (metal objects).
B. Hot-air oven: It is essential that hot air should circulate between the objects to be sterilized. Dry heat is reliable to sterilize all Glass wares which could tolerate a high temp. (160-180?C) such as tubes, flasks, measuring cylinders, all glass syringes, glass pipettes and glass Petri dishes. Metal instruments can also be sterilized by this method
Conditions of sterilization by hot air oven:
160?C for (2 hrs.) 120 min.
170 ?C for (1 hr.) 60 min.
180 ?C for (1/2 hr.) 30 min.