STERILIZATION AND ASEPSIS

INTRODUCTION Microorganisms are ubiquitous. Since they cause

contamination, infection and decay, it becomes

necessary to remove or destroy them from materials

or from areas. This is the objective of sterilization.

The methods of sterilization employed depend on

the purpose for which sterilization is carried out, the

material which has to be sterilized and the nature of

the microorganisms that are to be removed or

destroyed.

DEFINITION

Sterilization is defined as the process by

which an article, surface or medium is freed

of all microorganisms either in the vegetative

or spore state.

Sterilization is the total destruction of all

microbes including the more resilient forms

such as bacterial spores, mycobacteria

nonlipid viruses, and fungi.

Disinfection means destruction of all pathogenic organisms, or organisms capable of giving rise to infection.

Use of physical procedure or chemical agents to destroy most microbial forms, bacterial spores and other relative resistant organisms (eg: mycobacteria, nonlipid viruses, fungi); may remain viable.

Antisepsis

The term antiseptic is used to indicate the prevention of

infection, usually by inhibiting the growth of bacteria.

Chemical disinfectants can be applied safely to skin/

mucous membrane surfaces and are used to prevent

infection by inhibiting the growth of bacteria are called

antiseptics.

CLASSIFICATION OF INSTRUMENT STERILIZATION

The categorization of instrument depends on the contact with different tissue types to determine whether sterilization / disinfection is required. The categories are as follows.

1. Critical items : Instrument that touches sterile areas of the body enter the vascular system and those that penetrates the

oral mucosa. Eg : scalpel, curettes, burs

2. Semi – critical items : Instrument that touches mucous membrane and oral fluids but do not penetrate tissue, Eg.: saliva ejectors, radiograph, bite blocks, mouth micros etc.

3. Non critical items : Those items that does not come in contact with oral mucosa but are touched by saliva / blood contaminated hands while treating patient. Eg.: Chair light, switches, drawer pills etc. These should be properly disinfected.

INSTRUMENT PROCESSING

Holding solution

Rinse and dry

Instrument cleaning (ultrasonic)

Package

Rinse and dry

Seal

Sterilize

Store packages

Clinical use

METHODS OF CLEANSING INSTRUMENTS

1. Ultrasonic processing 2. Manual cleaningAdvantage of Ultrasonic processingIncreased efficiency in obtaining a high degree of cleanliness.Reduced danger to clinician from direct contact with potential

pathogenic microorganisms. Improved effectiveness for disinfection Elimination of possible dissemination of microorganisms through

release of aerosols and droplets, which can occur during scrubbing process.

Penetration into areas of the instruments where the bristles of a brush may be unable to contact.

Removal of tarnish.

Manual cleansing Ultrasonic processing is the method of choice, but when manual

cleaning is the only alternative, precaution must be taken to prevent contamination

CLASSIFICATION OF VARIOUS STERILIZATION AGENTS

A) Physical agents 1) Sunlight 2) Drying3) Dry heat : Flaming

Incineration Hot air

4) Moist heat : Pasteurization Boiling

Steam under normal pressure Steam under pressure

5) Filtration : Candles Asbestos pads Membranes

6) Radiation : ultra –violet radiation

Ionizing radiation 7) Ultrasonic and sonic vibrations

B) Chemicals 1. Alcohols : Ethyl, isopropyl,

Trichlorobutanal2. Aldehydes : Formaldehyde

Glutaraldehyde

3. Dyes 4. Halogens 5. Phenols 6. Surface –active agents 7. Metallic salts8. Gases : Ethyleneoxide,

formaldehyde, beta propiolactone

1) SUNLIGHT •Sunlight possesses appreciable bactericidal activity

•It is the sterilization which occurs under normal condition.

•The action is primarily due to its content of ultraviolet rays, most

of which, however, are screened out by glass and presence of

ozone in the outer regions of the atmosphere.

•Direct sunlight, as in tropical countryside where it is not filtered off

by impurities in the atmosphere, has an active germicidal effect

due to the combined effect of ultraviolet and heat rays.

•Simple and Grieg showed that, in India, typhoid bacilli exposed to

the sun on pieces of white drill cloth were killed in two hours,

whereas controls kept in the dark were still alive after six days.

Bacteria suspended in water are readily destroyed by exposure to

sunlight.

2) Drying

Moisture is essential for the growth of bacteria. Four-fifth by

weight of the bacterial cell consists of water. Drying in air has

therefore, a deleterious effect of many bacteria. This method

is unreliable and is only of theoretical interest spores are

unaffected by drying. 3) Heat Materials damageable by heat can be sterilized at lower temperatures, for

longer periods or by repeated cycles.

Moist heat is more effective than dry heat

Moist heat kills microorganisms probably by coagulation and

denaturing their enzymes and structural proteins, a process in

which water participates.

Sterilization ie killing of the most resistance spores, generally

requires moist heat at 121C for 15-30 minute.

Moist heat is effective at lower temperature. A properly

designed autoclave will effectively sterilize media and other

water – containing materials in sealed or unsealed bottles,

laboratory discards and porous packaged materials.

Killing effect of dry heat is due to protein denaturation,

oxidative damage and the toxic effect of elevated levels of

electrolytes.

Dry heat requires a temperature of about 160C for 60 minutes.

Dry heat is suitable for glasswares, instruments and paper-

wrapped articles not spoiled by very high temperatures, and for

water-impermeable oils, waxes and powders. Dry heat cannot

be used for water containing culture media.

DRY HEAT a) Flaming / Red Heat

b) Incineration

c) Hot air oven

Advantages

More convenient

Instruments are less likely to corrode

Do not require drying after sterilization

Disadvantages

Much harder to kill than when they are wet.

Has very little power of penetration and unless very high temperatures

are used, the method is slow.

Instruments need a considerable time to cool after sterilization and the

temper of metal instruments may be lost.

Used to sterilize glass ware, forceps, scissors, scalpels, all glass

syringes, swabs, measuring cylinders, some pharmaceutical

products such as liquid paraffin, dusting powder, greases.

Sterilization is achieved by dry heat at 160C for 45 minutes, 170C for 15

minutes,180C for 7½ minutes, 190C for 1½ minutes. These exposure

times are considered to be sufficient to kill the spores.

Hot air sterilizer should be fitted with a fan to provide forced air circulation

throughout the oven chamber, a temperature indicator, a control

thermostat, and timer, open mesh shelving and adequate wall insulation.

The oven is usually treated by electricity, with heating elements in the wall

of the chamber. Door interlocks should be fitted to ensure the heating cycle

will not start until the door is shut and that the door will not open while the

cycle is in progress.

The materials should be arranged in a manner which allows free circulation

of air in-between the objects.

The oven must be allowed to cool slowly for about 2hrs before the door is

opened since the glass ware may be cracked by sudden or uneven

cooling.

Moist heat can be employed At temperature below 100CAt a temperature of 100C (either in boiling water / in free steam) or At a temperature above 100C (in saturated steam under increased

pressure).

a) Moist heat at temperature below 100C

The best known Eg is in posturisation of milk.

The temperature employed is either 63C for 30min (the holder method) or

72C for 20 sec (the flash method) followed by cooling quickly to 130C or

lower. By these processes all nonsporing pathogens such as mycobacteria,

brucellae and salmonella that may be found in milk are destroyed.

Vaccines of nonsporing bacteria are heat inactivated in special vaccine

baths at 60C for one hour. Serum or body fluids containing coagulable

proteins can be sterilized by heating for one hour at 56C in a water bath on

several successive days.

Human immunodeficient virus (HIV) in serum may require 25 min at 56C for

inactivation.