STERILIZATION AND ITS PHYSICAL METHODS

STERILIZATION is a process of killing all micro organisms (including spores) on or in a material or object. Heating is the most common method used for sterilization.

Factors that determine the type of sterilization include:

1) Heat, 

2) Temperature.

Eg: pasteurization of milk holding period is 63° for 30 minutes or 72°c for 15-20 min.

For killing all non sporing pathogens. Eg: mycobacteria, brucellae, salmonella. 

3) Stages growth of organisms.

4) Nature of medium in which the organism       is suspended (air, gas, liquid)

5) Number of organisms present.

Thus making a substance free from all the microorganisms both in vegetative and sporing states. It is the most important procedure and has major share in success of surgical management. 

Sterilization and disinfection can be achieved by using heat filtration, chemical or radiation etc.. Some are discussed below.

Methods of sterilization are: 

1) Physical Methods 

2) Chemical Methods 

Some general used laboratory method for sterilization are:

1) Dry heat

2) Flame sterilization

3) Autoclaving.

PHYSICAL METHODS:

1) Sunlight: Action primarily due to UV rays, however effects vary due to places .

Eg: In tropical countries, the germicidal effects is better than four seasoned countries. Bacteria in water are readily destroyed by sunlight.

2) Drying: Moisture is essential for the growth of bacteria. Drying in air has deleterious effect on bacteria. However, spores are unaffected and therefore it is not really reliable.

3) Heat: Most reliable method of sterilization and should be the method of choice. It can be divided into three:

A) Dry Heat:

     I) Flaming: heating over fire till they                     become red hot. Instruments like point           forceps, spatulas, inoculatory loops and           wires.

         Inoculatory loops is better dipped in                 disinfect first before flaming to prevent           spattring. 

     II) Incerination: It is a process that                        involves combustion of organic                          substances contained in waste                            materials.

     Items: contaminated clothes, animal                 carcasses and pathological material and         PVC polythene can be dealt.

    III) Hot air oven: These are electrical                      devices used in sterilization.

          The oven uses dry heat sterilized                      articles. Generally they can be                            operated from 50 to 300°C.

          There is a thermostat controlling the                temperature. This is the most widely                used method of sterilization by dry                  heat. 

    Items: Glassware, forceps, scissors,                                 scalpels, all glass syringes, swabs,                     liquid paraffin, dusting powder, fat,

                 greases.

    Precautions:

    - Glassware should be dry.

    - Oven should not be overloaded. 

    - Articles should be arranged in a manner        to allow free circular of air.

    -  Door of the oven should be opened                   when it cools down. (2 hours).

   IV) Moist heat:

         Boiling: ( Temp. At 100°C)

         Not recommend for sterilization but                 disinfecting, sterilization may be                       promoted by addition of 2% sodium                 bicarbonate to water. 

         Holding period: 10-30 min.

      

         Steam at atmospheric pressure 

         (Temp at 100°C) :

         This is used to sterilize culture media.

         It is an inexpensive method.

         The first exposure kills the vegetative 

         bacteria then the second exposure kills

         the vegetative bacteria that develops 

         from spores.

    

         Steam under pressure:

         Autoclave/ Steam sterilizer- Autoclave 

         is a device that uses steam to sterilize

         equipment and other objects. This mean

         that all bacteria, viruses, fungus and 

         spores are inactivated. 

         However, prions may not be destroyed

         in autoclaving. Holding period varries.

         Temperature: Between 108°C and 147°C.

4) Filtration: Helps to remove bacteria from heat labillic liquids.

A) Candle filters: Used for purification of water for industrial and drinking purpose.

They are of two types:

-Unglazed ceramic filters.

-Diatomaceous filters.

B) Asbestos Filters: Disposable, single used disc. Tend to alkaline filtered liquids. Usage is discouraged because of its carcinogenic property.

C) Sinerated Glass filters: Has low absorptive properties and are very brittle and expensive.

D) Membrane Filters: Made of cellulose easter or other polymers.

Usually used for water purification and analysis, sterilization and sterility testing and preparation of solutions for parenteral use.

5) Radiation: There are two types of radiation:

A) Non- Ionizing radiation: 

- Infrared used for massive mass sterilization of pre-packed items such as syringe and cathaters.

- uv

-used for disinfecting the enclosed area such as entry ways, operation theater and labs.

B) Ionizing radiation:

- Gamma rays

 i) X-rays: 

    Used for sterilizing plastics, syringes, swabs, Catheters, animal feeds, cardboard, oils, gresses fabric and metal foils.

Application of sterilization: 

FOOD: Sterilization in foods is one of the biggest step in food industry. This slowed the decay of foods and various liquids preserving them for safe consumption for a longer time then was before.

Medical and surgery: 

Surgical instruments and medicines that enter already an aseptic part of the body ( blood stream) must be sterile. Eg: scapels, hypodermic needles and artificial pacemaker and also essential in manufacture of parenteral pharmaceuticals.

Spacecraft:

There are strict international rules to protect the contamination of solar system bodies from biological material from earth. 

Many components of instruments used on spacecrafts can not withstand very high temperature. So techniques not requiring excessive temperature are used as tolerated, including  heating to at least 120° c (248°f ) , chemical sterilization, ultraviolet, irradiation and oxidation.

In laboratories: 

Many researchers and students performing equipments in lab also perform sterilization for the equipments further use.

 

This was all about sterilization and its physical methods and applications. Stay tuned for chemical methods on sterilization in the next post.