Sterilization and Disinfection

• Lecture: Sterilization And Disinfection

D. Faten Naeem Abass

Sterilization describes a process that destroys or eliminates all forms of microbial life and is carried out in health-care services by physical or chemical methods.
1-Heat
Moist heat(Steam) sterilization
• heat sterilization by autoclave.
• 121–134 °C (250–273 °F) under pressure for15 minutes,
• This method is a faster process than dry heat sterilization.
• Used for culture media
• Dry heat sterilization
• The destruction of microorganisms by a hot air oven
• at least two hours at 160 °C (320 °F).
• it can be used on powders and other heat-stable items (steel objects).

• Flaming

• Flaming is done to inoculation loops and straight-wires in microbiology labs for striking .
• Leaving the loop in the flame of a Bunsen burner until it glows red
• This is commonly used for small metal or glass objects, but not for large objects


• Incineration
Incineration is a waste treatment process that involves the burning of organic substances contained in waste materials.
This method also burns any organism to ash and kill off any microorganisms that may be on an inoculating loop or wire.
It is used to sterilize medical and other biohazardous waste before it is discarded with non-hazardous waste.

Tyndallization

John Tyndall
process designed to reduce the level of activity of sporulating bacteria that are left by a simple boiling water method.
 The process involves boiling for a period (typically 20 minutes) at atmospheric pressure, cooling, incubating for a day, and then repeating the process a total of three to four times.
The incubation periods are to allow heat-resistant spores surviving the previous boiling period to germinate to form the heat-sensitive vegetative (growing) stage, which can be killed by the next boiling step.

2-Chemical sterilization

•Ethylene oxide : Ethylene oxide (EO, EtO) gas treatment is one of the common methods used to sterilize, pasteurize, or disinfect items because of its wide range of material compatibility. It is also used to process items that are sensitive to processing with other methods, such as radiation (gamma, electron beam, X-ray), heat (moist or dry), or other chemicals.
Ethylene oxide treatment is the most common chemical sterilization method, used for approximately 70% of total sterilizations, and for over 50% of all disposable medical devices.

•Nitrogen dioxide

Nitrogen dioxide (NO2) gas is a rapid and effective sterilant for use against a wide range of microorganisms, including common bacteria, viruses, and spores.
•Ozone
Ozone is used in industrial settings to sterilize water and air, as well as a disinfectant for surfaces.
•Glutaraldehyde and formaldehyde
Glutaraldehyde and formaldehyde solutions (also used as fixatives) are accepted liquid sterilizing agents, kill all spores in a clear liquid can take up to 22 hours with glutaraldehyde and even longer with formaldehyde.
•Hydrogen peroxide
Hydrogen peroxide, in both liquid and as vaporized hydrogen peroxide (VHP), is another chemical sterilizing agent. Hydrogen peroxide is a strong oxidant, which allows it to destroy a wide range of pathogens. (VHP) is used to sterilize large enclosed and sealed areas, such as entire rooms.
Although toxic, VHP breaks down in a short time to water and oxygen.


3-Radiation sterilization
•Non-ionizing radiation sterilization
Ultraviolet light irradiation (UV) is useful for sterilization of surfaces and some transparent objects (absorb)
UV irradiation is routinely used to sterilize the interiors of biological safety cabinets.
•Ionizing radiation sterilization
Gamma radiation is very penetrating, and is commonly used for sterilization of disposable medical equipment, such as syringes, needles, cannulas and food.
Electron beam processing is also commonly used for sterilization. Electron beams provide a much higher dosing rate than gamma or X-rays.
High-energy X-rays allow irradiation of large packages and pallet loads of medical devices.

4-Sterile filtration

Fluids that would be damaged by heat, irradiation or chemical sterilization, such as drug solution, can be sterilized by microfiltration using membrane filters that are commonly made from materials such as mixed cellulose ester or polyether sulfone (PES).

Disinfection describes a process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects.

Levels of disinfection:

These levels are based on the microbicidal effect of the chemical agents on the microorganisms and can be:
High-level disinfection (HLD): This is carried out with liquid chemical agents that eliminate all of the microorganisms. Examples are ortho-phthaldehyde, glutaraldehyde, per acetic acid, chlorine dioxide, hydrogen peroxide and formaldehyde.

Intermediate-level disinfection (ILD): This is carried out using chemical agents that eliminate vegetative bacteria and some bacterial spores. This includes the phenol group, sodium hypochlorite, cetrimide and benzal konium chloride.


Low-level disinfection (LLD): This is carried out by chemical agents that eliminate vegetative bacteria, fungi and some viruses within a short period of time (less than 10 minutes). One example is the group of quaternary ammoniums.

Disinfection methods

Disinfection is one of the oldest procedures in the hospital environment. It was originally used to eliminate microorganisms from the environment and to sterilize hands. There are two disinfection methods: physical and chemical.
1-Physical methods
• Pasteurization
This method was originally used by the French Louis Pasteur.
This process is used to carry out HLD, by bringing water to 77 ºC for approximately 30 minutes.
This destroys all microorganisms except bacterial spores.

• Boiling

• This method uses boiling water at very high temperatures to achieve disinfection.
• For example, during HLD instruments are boiled in a covered container for 15 to 20 minutes,
• Ultraviolet radiation (UV)
• This method inactivates microorganisms in the range of 240–280 nm. It acts through the denaturation of nucleic acids.

2-Liquid chemical methods

This is the most frequently utilized method in our hospital system and multiple germicidal agents exist in liquid form. The principal disinfectants used in the hospital area are: ortho-phthaldehyde, glutaraldehyde, chlorine and chlorinated compounds, formaldehyde, hydrogen peroxide, per-acetic acid, phenols and quaternary ammoniums.

Factors that affect the efficacy of both disinfection and sterilization include:

• prior cleaning of the object;
• organic and inorganic load present;
• type and level of microbial contamination;
• concentration of and exposure time to the germicide;
• physical nature of the object (e.g., crevices, hinges, and lumens);
• presence of biofilms;
• temperature and PH of the disinfection process;
• and in some cases, relative humidity of the sterilization process (e.g., ethylene oxide).


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