sterilization

DEFINATIONSCLEANING - It is a process which removes

visible contamination but does not necessarily destroy micro organisms.

ASEPSIS -Term used to describe methods which prevent contamination of wounds and other sites

ANTISEPSIS - It is the procedure or application of an antiseptic solution or an agent which inhibits the growth of microorganisms, while remaining in the contact with them.

DISINFECTION - it is a process which reduces the number of microorganisms to an acceptable level but may not inactive some viruses and bacterial spores.

STERLIZATION any process that effectively kills or eliminates transmissible agents (such as fungi, bacteria, viruses, spore forms, etc.) from a surface, equipment, article of food or medication, or biological culture medium.

Sanitizing - process of reducing the number of microorganisms

Decontamination - process that removes pathogenic microorganisms from an object to make it safe to handle.

HAND WASHING

• Three types of hand washing-

– Social hand washing– Clinical hand washing– Surgical hand washing

Social hand washing

• Recommended following social-type contact with clientsafter covering a cough or sneeze.

• A plain liquid soap is often used.

Clinical hand washing

• A clinical hand wash is used before clinical procedures on clients, when a client is being managed in isolation, or in outbreak situations.

• An anti-microbial soap, containing an antiseptic agent, is used.

Surgical hand washing

• A surgical hand wash is required before any invasive or surgical procedure requiring the use of sterile gloves.

• An antimicrobial skin cleanser, – usually containing chlorhexidine or – detergent-based povidone-iodine, is used.

Surgical Scrubbing :The purpose is to reduce resident and transient skin flora (bacteria) to a minimum.

hand scrubbing

sterile gown provide

wearing of sterile gloves

These provide patient with the best possible barrier against pathogenic bacteria in the environment and against bacteria from the surgical team.

The following steps comprise the generally accepted

method for the surgical hand scrub-

To achieve sterilization of any instrument three definite stages are to be completed-

Pre sterilization cleaning Sterilization Aseptic storage

Sterilization of any instrument

Presterilization cleaning• Objective-

Removal of the organic matters, blood and saliva which provide protective barrier for microorganisms and prevents its destruction.

• There are three methods for cleaning1. -Manual2. -Ultrasonic3. -Mechanical washing

MANUAL CLEANING

• Simplest and the cheapest method, – time consuming and – difficult to achieve.

• heavy duty gloves and glasses must be worn to protect needle stick injury and to protect eye.

• Material used for manual cleaning1. Soaps2. Detergents

ULTRASONIC CLEANINGPrinciple- conversion of electrical energy into vibratory sound waves which pass through a soap solution containing the instrument.

Used mainly for bone files, bone cutter, artery forceps, saw etc.

MECHANICAL WASHINGPrinciple- High-pressure jets of water with or without a detergent which removes debris from instrument.

Small instrument like blade are not suitable for this type of cleaning.

Sterile Techniques

Sterile TechniquesSTERILISATION: any process that effectively kills or

eliminates transmissible agents (such as fungi, bacteria, viruses, spore forms, etc.) from a surface, equipment, article of food or medication, or biological culture medium.

Sterilization can be achieved through application of heat, chemicals, irradiation, high pressure or filtration.

STERILISATION Types

I. CHEMICAL METHODSII. PHYSICAL METHODSA. Heat :

1. Dry heat2 Moist heat

B. Radiations1. Ultraviolet radiations2. Ionizing radiations

C. Filtration

Chemical sterilization

Chemical sterilization• Sterilization includes both liquid and gas chemicals

Mechanism of action of chemical disinfectants :The mechanism of action of most of the chemicals are

nonspecific and complex but most of them effect microorganisms by one of the following mechanisms.

1. Cell membrane injury.

2. Denaturation.

3. Interactions with functional groups of proteins.

1. ALDEHYDE COMPOUNDS

a. Formaldehyde:

A broad-spectrum antimicrobial agent, used for disinfection,

limited sporicidal activity.

Hazardous substance, inflammable and irritant to the eye, skin and respiratory tract.

b. Glutaraldehyde:

It is a high level disinfectant A solution of 2% glutaraldehyde requires

20 minutes for disinfection; 6 to 10 hours of immersion for sterilization.

2. ALCOHOLS

Act by denaturing bacterial proteins.

ethanol

Solutions of 70% ethanol are more effective than higher concentrations, as the presence of water speeds up the process of protein denaturation .

Frequently used for skin antisepsis prior to needle puncture.

Isopropyl alcohol is

preferred as it is a better fat solvent,

more bactericidal

less volatile.

Used for disinfection of clinical thermometer .

3. IODOPHOR COMPOUNDS

iodophor compounds are the most effective antiseptics.

Iodine is complexed with organic surface-active agents, such as, polyvinylpyrrolidone (Betadine, Isodine).

Their activity is dependent on the release of iodine from the complex.

These compounds are effective against most bacteria, spores, viruses, and fungi.

These are the most commonly used surface disinfectants along with hypochlorite.

4. Biguanide : Most commonly used biguanide compound is

chlorhexidine.

It is a powerful non-irritating antiseptic

disrupts bacterial cell membrane.

It persists on skin for longer period of time and that is why it is extensively used

for surgical scrubbing,

neonatal bath,

mouth wash and

a general skin anti-septic.

Vapors and Gases

• formaldehyde, beta-propiolactone and ethylene oxide are not routinely used in laboratory sterilization practices.

• These sterilants are used in hospitals and commercial facilities where closed systems controlling temperature, humidity, and concentration are required to achieve sterilization using these agents.

Heat sterilization

Two methods of Heat sterilization1. Dry Heat sterilization

2. Moist Heat sterilization

Dry Heat sterilization

Dry heat, as the name indicates, utilizes hot air that is either free from water vapour, or has

very little of it, and moisture plays a minimal or no role in

the process of sterilization

Mechanism of killing by dry heat

1. Dry heat kills the organisms by destruction of essential cell constituents

2. Killing of the most resistant spores by dry heat requires a temperature of about 160 °C for 60 minutes

3. Dry heat is employed for glassware; syringes, metal instruments and paper wrapped goods, which are not spoiled by high temperatures.

4. It is also used for anhydrous fats, oils and powders that are impermeable to moisture.

METHODS OF STERILIZATION BY DRY HEAT

1. RED HEAT2. FLAMING3. HOT AIR OVEN4. NON IONIZING RADIATION

1.RED HEAT

• Inoculating wires, • points of forceps and spatulas are sterilized by

holding them in the flame of Bunsen burner until they are seen to be red-hot.

2. FLAMING

• This method is used for sterilizing scalpel, mouth of culture tubes, glass slides etc. It involves passing of an article through Bunsen flame without allowing it to become red-hot.

3. HOT AIR OVEN• This is the main means of sterilization by dry

heat. Exposure at a temperature of 160 °C for 1 hour is generally employed.

Hot air ovens are electrical devices used in sterilization. There is a thermostat controlling the temperature. These are digitally controlled to maintain the

temperature. Their double walled insulation keeps the heat in and conserves energy,

An air circulating fan helps in uniform distribution of the heat. These are fitted with the adjustable wire trays or aluminium trays and may have an on/off rocker switch, as well as indicators and controls for temperature and holding time. The capacities of these ovens vary.

• UV light and infrared• Affect 3-D structure of proteins and nucleic

acid

4. Non ionizing radiation

Moist Heat sterilization

METHODS OF STERILIZATION BY MOIST HEAT

Moist heat can be employed at1. Temperature below 100 °C2. Temperature of 100 °C3. Temperature above 100 °C

MOIST HEAT BELOW 100 °C

EXAMPLE: Pasteurization of milk In Pasteurization of milk the temperature

employed is either 63 °C for 30 minutes or 72 °C for 20 seconds.

All nonspore forming pathogens in milk like Salmonellae, M.tuberculosis are killed.

MOIST HEAT ABOVE 100°C

Sterilization in an autoclave1. Autoclaving is the most reliable method. It is

the method most widely used for sterilization of culture media and surgical supplies

2. When water is boiled within a closed vessel at an increased pressure, the temperature at which it boils and the steam it forms will rise above 100 °C. This principle is used in the autoclave

Steam sterilizationA widely-used method for moist heat

sterilization is the autoclave. Autoclaves commonly use steam heated to

121 °C or 134 °C. To achieve sterility, a holding time of at least

15 minutes at 121 °C or 3 minutes at 134 °C is required.

Proper autoclave treatment will inactivate all fungi, bacteria, viruses and also bacterial spores, which can be quite resistant. It will not necessarily eliminate all prions. For prion elimination, various

recommendations state 121–132 °C (270 °F) for 60 minutes or 134 °C (273 °F) for at least 18 minutes. The prion that causes the disease (strain 263K)

is inactivated relatively quickly by such sterilization procedures

Mechanism of killing by moist heat

1. Moist heat kills the organisms by denaturing their enzymes and structural protein.

2. Sterilization by moist heat of the most resistant spores generally requires 121 °C for 15-30 minutes.

3. Moist heat is used for the sterilization of culture media, and all other materials through which steam can penetrate

FACTORS INFLUENZING STERILIZATION BY HEAT

1. The temperature and time: they are inversely related, shorter time is sufficient at high temperatures.

2. Number of microorganisms and spores: 3. Depends on the species, strains and spore4. Depends on the nature of material: a high content of

organic substances generally tends to protect spores and vegetative organisms against heat.

5. Presence of organic or inorganic disinfectants facilitates killing by heat

6. pH also plays an important role in the killing of microorganisms

MERITS AND DEMERITS OFHEAT STERILIZATION

Advantages of heat sterilization1. Sterilization is very effective2. Instruments are standardized to deliver the

required effective heat3. Heat deliver system can be monitored

effectively with various controls like pressure gauge, temperature meters etc.

Disadvantages of heat sterilization

1. Steam impermeable materials like fats, oils and powders can not be sterilized by autoclaving.

2. Heat sensitive materials can not be sterilized by heatExamples:1. Serum can not be sterilized2. Antibiotics3. Plastic materials4. Vaccines5. Rubbers3. Presence of organic matters interfere with effective

sterilization4. Dangers of explosion when high pressure is used

STERILIZATION BY FILTRATION

STERILIZATION BY FILTRATION1. When fluids are passed through bacteria stopping

filters, they are made free from bacteria.2. It is useful for making preparations of soluble

products of bacterial growth such as toxins3. Liquids that would be damaged by heat such as

serum and antibiotic solutions can be sterilized by filtration

Aseptic storageThe maintenance of sterility during transportation and storage is of utmost importance.

• Instruments are kept wrapped until ready for use .

• To reduce the risk of contamination, sterile packs must be handled as little as possible.

• Sterilized packs should be allowed to cool before storage; otherwise condensation will occur inside the packs.

• To prevent contamination from rodents, ants, and cockroaches, the store must be subjected to adequate pest control .

• Sterile packs must be stored and issued in correct date order. The packs, preferably, are stored in drums which can be locked.