STERILIZATION

STERILIZATION

Definition:

It is a process by which articles surfaces or medium is made free of all microorganisms either in the vegetative or spore form.

DISINFECTION:

It means the destruction of all pathogen or organism capable of producing infection but not necessarily spores.

ANTISEPTICS:

These are chemical disinfectant which can be safely be applied to live tissues and are used to prevent infection by inhibiting the growth of micro-organisms.

ASEPSIS:

The technique by which the occurrence of infection into an uninfected tissue is prevented.

OBJECT OF STERILISATION:-

The aim of sterilization is to remove destroy microorganisms from material or from surfaces.

USES OF STERILISATION:-

1)For sterilization of materials, instruments used in surgical and diagnostic procedures.

2)For media and reagents used in the microbiology laboratory.

3)In food and drug manufacturing to ensure safety from contaminating organisms.

I PHYSICAL METHODS:-

1. SUNLIGHT:-

Sunlight is a natural method of sterilization in case of water in tanks rivers and lakes due to its active germicidal effect of UV-rays.

2.HEAT:-

It is the most reliable and commonly used method. It can be done in 2-ways.

(A) Dry heat sterilization:-

Principle- Dry heat kills the organisms by denaturation of bacterial protein, oxidative damage and by the toxic effect of elevated levels of electrolytes.

METHODS:-

a) Red heat:- Inoculating wires, or loops, tips of forceps and needles are held in the flame of a Bunsen burner till they become red hot.

b) Flaming:- Glass slides, scalpels, and mouth of cultures tube are passed through Bunsen burner flame without allowing them to become red hot.

c) Incineration:- Infective materials are reduced to ashes by burning. 

d) Hot Air Oven:- (worked or principle of dry heat)

Method:-

The oven is electrically heated and is filled with a fan to ensure even distribution of hot air in the chamber.

It is also filled with a thermostat that maintains the chamber air at a chosen temperature.

Temperature and Time:-160°C for two hours is required for sterilization.

Uses:-

It is used for sterilization of -

• Glasswares- glass syringes, Petri dishes flasks, test tube, Pipettes.
• Surgical Instruments -Scalpels, scissors, etc
• Chemical -Liq. Paraffin, fats, etc.

 Precautions:-

• It should not be overloaded.
• The material should be arranged in a manner to allow free circulation of air.
• Materials should be perfectly dry properly.
• The oven must be allowed to cool before opening the door.
• Petri dishes and pipettes should be wrapped in paper.

(II) Moist heat sterilization:-

a) At a temperature below 100°C

• Pasteurization of milk.
• Inspissation.
• Vaccine bath.
• Low-temperature steam formaldehyde (LTSF) Sterilization.

b) At a temperature of 100°C

• Boiling.
• Tyndallisation.
• Steam steriliser at 100°C for 90min.

c) At a temperature above 100°C

• Autoclave.

SOME ARE EXPLAIN BELOW-

a) Pasteurization of milk:-

Two types of method, holder method (63°c for 30 minutes) and flash method (72°c for 20 sec) followed by cooling quickly to 13°c or lower) are used.

All non-sporing pathogens such as mycobacteria, salmonellae are killed.

b) Inspissation:-

Some serum or egg media are rendered sterile by heating at 80-85°c temperature for half an hour daily on three consecutive days. This process of sterilization is called inspissation.

c) Boiling:-

Boiling for 10 to 30 minutes may kill most of the vegetative forms but many spores without boiling for a considerable time.

d)Tyndallisation:- 

Steam at 100°c for 20 minutes on three successive days is used. This is known as tyndallisation or intermittent sterilization. The instruments commonly used is Koch's or Arnold's steam sterilizer.

AUTOCLAVE:-

Modified pressure cooker or boiler.

Principle:-

Steam above 100°C or saturated steam has a better killing power than the dry heat. Saturated steam can penetrate porous materials easily. When steam comes into contact with a cooler surface it condenses to water and liberates it's latent heat to that surface. This condensed water produces moist conditions for killing the microbes.

Components of Autoclave:-

It consists of-

• A vertical /horizontal cylinders - made up of gunmetal or stainless-steel.
• A lid- fastened by screw clamps.
• Lid bear discharge tap for steam and air.
• A pressure gauge
• A safety value.

Procedure:-

• The cylinder is filled with sufficient water.
• Material to be sterilized is placed on the ray.
• The lid is closed with a discharge tap open.
• Safety value is adjusted to require pressure.
• After boiling water, the steam and air mixture is allowed to escape. The discharge tap is now closed.
• When the inside steam pressure reaches the desired set level the safety valve is open. Holding period (15 min.).
• After holding period the heating is stopping and autoclave allowed to cool till the pressure becomes equal to atmospheric pressure.
• Discharge tap is open slowly and the air is allowed to enter the autoclave.
• The lid is now opened and the sterilized material is removed.

Sterilisation Condition:-

• Temperature - 121°C.
• Chamber pressure - 15 lbs per eq. Inch.
• Holding time - 15min.

Uses:-

• To sterilize culture media, rubber materials gowns, dressing, gloves, etc.
• It is used for materials which cannot withstand the higher temperature.

Precaution:-

• Materials should be arranged properly to allow free circulation of steam.
• The air must be allowed to escape from the chamber.

3.FILTRATION:-

This method of sterilization is useful for the substances which get damaged by heat procedure eg. sera, sugar, antibiotic solutions etc.

Types of filters:-

i. Candle filters.

ii. Asbestos disc filters.

iii. Sintered glass filters.

iv. Membrane filters.

v. Air filters.

vi. Syringe filters.

Uses of filtration:-

i. Purification of water.

ii. To sterilize sera, sugar and antibiotic solution.

iii. Sterilization of hydraulic fluid.

iv. Separation of toxins and bacteriophages from bacteria.

4.Radiations:-

Two types of radiations are used-

(I) Ionising Radiation->

It includes Y-rays, X-rays and cosmic rays. They have very high penetrating power and are highly that to the cells. They damage the DNA of the cells.

Y-radiations from a cobalt 60 sources are commercially used for sterilization of disposable items such as plastic syringes, swabs, culture, cannulas, etc. This method is known as cold sterilization.

(II) Non-ionizing Radiations-

It includes UV (ultraviolet) and Infra-red radiation. UV-radiation has marked bactericidal activity. Infrared is used for the rapid mass sterilization of syringes and catheters.

II.CHEMICAL METHODS:-

A variety of chemical agents are used as antibiotics and disinfectants-

1. ALCOHOLS:-

They act by denaturing bacterial protein and rapidly kill bacteria including tubercle bacilli. They have no sporicidal or virucidal activity. Ethyl alcohol and isopropyl etc are most frequently used.

Uses-> They used mainly as skin antibiotics.

2.ALDEHYDES:-

i. Formaldehyde- It is markedly bactericidal, sporicidal and virucidal.

It is used both as an aqueous solution or in a gaseous form.

Uses->

• To sterilize bacterial vaccines.
• Preservation of tissues for histological examination.

ii. Glutaraldehyde- It is effective against bacteria fungi and viruses.

Uses->

• For sterilization of cystoscopes, endoscopes, and bronchoscopes.
• To sterilize plastic endotracheal tube, face mask, anesthetic tubes, and metal instruments.

3. PHENOLS:-

Phenol has a lethal effect due to cell membrane damage and thus causes Lysis. It has bactericidal action.

i. Cresols- Lysol is a solution of cereals used for sterilization of glassware, floors, etc.

ii. Chlorhexidine- Savlon widely used in wounds preoperative disinfection of the skin.

iii.Chloroxylenol- It is an active ingredient of Dettol.

4.HALOGENS:-

Chlorine and iodine are two commonly used disinfectants. These are bactericidal and are effective against sporing bacteria and viruses.

5.Oxidizing Agents:-

i. Hydrogen peroxide- It is effective against most organisms at a concentration of 3-6%.
ii. Peracetic acid- It is one of the high-level disinfectants. It is used in a plasma sterilization procedure.
iii.Plasma sterilization- Plasma refers is any gas which consists of electrons ions or neutral particles. The formation of low-temperature plasma requires several devices used for surgical instruments.

6.Salts:-

Salts of heavy metals have a toxic effect on bacteria. The salts of copper, silver, and mercury are used as a disinfectant.

7.Surface-active Agents:-

The substance which alters energy relationships at interfaces producing a reduction of surface tension are known as surfactants.