Disinfectionand

Sterilization

Disinfection It is the Killing of most microbial forms. Some

resistant forms of organisms e.g. bacterial spores, mycobacterium , viruses, fungi may remain viable.

Disinfection can achieved by boiling, pasteurization ,UV rays and chemical agents.

Antisepsis (by antiseptics) Inhibition or elimination of microbial

forms on the skin or living tissue.

We can use chemical agents like ethyl alcohol.

It is not suitable for systemic administration.

Germicides Germicides are chemical agents.

They are used for Killing of microbial forms but spores may remain viable.

Sporicide It is Germicide able to killing bacterial

spores.

Cleaning It is the removal of visible dust, dirt and

foreign material by water and soap. It usually precede disinfection and

sterilization .

Decontamination It is a general term applied to any

procedure by which microorganism are reduced to a level where the equipments is safe for handling.

sterilization Sterilization is the Killing of all living forms of

microbes (bacteria, fungi and viruses)

Mthods of sterilization

I-Heat sterilization (moist or dry)

II-Low temperature sterilization

III- sterilization by radiation

IV- sterilization by Filtration

Is the most practical efficient and inexpensive method of sterilization, it can be used in two forms: moist heat and dry heat

A: Moist heat Is much more efficient than

dry heat, because it kills the microbes by coagulation and denaturing of their enzymes and structural protein.

I-Heat Sterilization

a-Moist heat at a temperature below 100oC

An example is pasteurization of milk by heat at either 63oC for 30min or at 72oC for 20sec and immediately cooling to below 10oC.

Pasteurization can destroy all non- spore forming pathogens.

b- Moist heat at a temperature of 100oC (boiling) Boiling at 100oC for 20Min. to kill all

vegetative bacteria and hepatitis B virus but not all bacterial spore . This method may be used for disinfection of surgical equipment).

c- Moist heat at a temperature above 100oC (autoclave)

• The sterilizing agent is saturated• water steam under high pressure.

• Equipment used called: Autoclave

• Saturated steam should be free from air.

• At 2bar (atmospheric pressureX2), the temperature is 121oC and strilization time is 20-30 min

• At 3bar the temperature is 134oC and sterilization time 3-6min

• The autoclave is used for sterilization of culture media, surgical instruments, dressings, gowns, cotton, gauze.

• Advantages of moist heat• 1-Steam has high penetrating power. • 2--Not toxic• 3-Low cost and not time consuming.

• Disadvantage of moist heat• 1- Some items can not withstand the high • temperature of steam• 2- Not suitable for powder and oils.

B-Dry Heat• It is kill the microorganisms by destructive

oxidation of essential cell constituents• it is less efficient than moist heat.

• Methods of dry heat1-Incineration used for tratment of dead animals, infectious

hospital wastes, surgical dressings, needles.2-Red heat Exposing wires, loops, points of forceps to flame until become red.

3-Hot air oven Oven is an double walled metal chamber

heated by electricity, to a constant temperature

Sterilization time and temperature: 2 hr 160oC for 2Hr One hr 170oC. 30 Min at 180oC

Hot air oven is used for sterilization of: glassware, ointments, powders, oils, and

metallic instruments

II-Low temperature sterilization1- By GasEthylene oxide 450-1200 mg/L at 56oCTime of exposure varies from 3-6 hours. Its Advantage is capability of sterilizing the

instruments that cannot be subjected to steam or hot air oven without any damage .

Disadvantage is :long duration ,High cost and toxicity.

2-By liquids1-PERACETIC ACID 0.2%2-GLUTARALDEHYDE (Cidex) 2%

III-III-Sterilization by Sterilization by RadiationRadiation 1-Gamma rays 1-Gamma rays

2-2- ββ-rays-rays (High- energy electrons) (High- energy electrons)

These are used for sterilization of Heat These are used for sterilization of Heat sensitive items like:sensitive items like:

Prepacked disposable plastic items like plastic Prepacked disposable plastic items like plastic syringe ,catheters ,gloves, surgical suture, IV sets syringe ,catheters ,gloves, surgical suture, IV sets and plastic Petri dishes.and plastic Petri dishes.

• 3-Ultra Violet light 3-Ultra Violet light • It is present in sun raysIt is present in sun rays• It is produced artificially byIt is produced artificially by

mercury lamps mercury lamps • It has weak penetrating powerIt has weak penetrating power• It is used to reduce the number of bacteria in It is used to reduce the number of bacteria in

air and for surface disinfection in certain area air and for surface disinfection in certain area e.g. operation room , lab safety cabinet.e.g. operation room , lab safety cabinet.

IV-IV-Sterilization by Sterilization by FiltrationFiltration•This is the a mechanical This is the a mechanical

exclusion of microorganisms exclusion of microorganisms from biological fluids which from biological fluids which are sensitive to heat as are sensitive to heat as serum, plasma, hormones, serum, plasma, hormones, vitamins.vitamins.

• Filters used have pore size Filters used have pore size of less than of less than 0.45um0.45um..

•Viruses and bacteria as Viruses and bacteria as mycoplasma pass through mycoplasma pass through filtersfilters