Microsoft Word - Cold Sterilization Unidad 4

8/14/2019 Microsoft Word - Cold Sterilization Unidad 4

1/6

COLD STERILIZATION

A-CHEMICAL AND GAS STERILIZATIONChemicals used for sterilization include the gases ethylene oxide and

formaldehyde, and liquids such as glutaraldehyde. Ozone, hydrogen

peroxide and peracetic acid are also examples of chemical sterilization

techniques. These techniques, however, do not offer the same degree of

sterility assurance as heat methods, and are generally reserved for

temperature sensitive items.Ethylene oxide (ETO) is the most commonly used form of chemical

sterilization. Due to its low boiling point of 10.4C at atmospheric pressure,

it behaves as a gas at room temperature. It reacts chemically with amino

acids, proteins, and DNA to prevent microbial reproduction. The

sterilization process is carried out in a specialized gas chamber. After

sterilization, products are transferred to an aeration cell, where they remain

until the gas disperses and the product is safe to handle, as it is toxic,

mutagenic, and carcinogenic.

ETO does not penetrate glass, metals and crystals. It is used for cellulose and

plastics irradiation, usually in sealed packages. Ethylene oxide can be used

with a wide range of plastics (e.g. petri dishes, pipettes, syringes, medical

devices, etc.) and other materials without affecting their integrity. It is

suitable for all antibiotics and hormones, surgical dressings and thermolabile

powders.

An ethylene oxide

sterilization gas chamber.


2/6

Ozone sterilization uses oxygen that is subjected to an intense

electrical field that separates oxygen molecules into atomic oxygen, which

then combines with other oxygen molecules to form ozone.Ozone is used as a disinfectant for water and food. It is used in both gas and

liquid forms as an antimicrobial agent in the treatment, storage and

processing of foods, including meat, poultry and eggs. Many municipalities

use ozone technology to purify their water and sewage. Ozone is used to

disinfect swimming pools, and some companies selling bottled water use

ozonated water to sterilize containers.

An ozone sterilizer for use in the hospital or other medical environment.

B-RADIATION STERILIZATION

Irradiation: usually destroys or distorts nucleic acids.

Ultraviolet light is commonly used to sterilize the surfaces of

objects, although x-rays, gamma radiation and electron beam radiation are

also used.

I) Ultraviolet lamps:

Are used to sterilize workspaces and tools used in microbiology laboratories

and health care facilities. Also used for sterilization of air. UV light at

germicidal wavelengths (two peaks, 185 nm and 265 nm) inhibits DNA

replication (even though the organism may not be killed outright, it will not


3/6

be able to reproduce). However, since microorganisms can be shielded from

ultraviolet light in fissures, cracks and shaded areas, UV lamps should only

be used as a supplement to other sterilization techniques.

An ultraviolet sterilization cabinet.

II) Ionizing radiation:

Gamma radiation and electron beam radiation are forms of ionizing radiation

used primarily in the health care industry. Ionizing radiation work by

splitting genes resulting in cell death.

a- Gamma rays, emitted from cobalt-60, are similar in many ways to

microwaves and x-rays. Gamma rays are highly effective in killing

microorganisms and do not leave residues or have sufficient energy to

impart radioactivity. Suitable for sterilization of deep articles.

b- Electron beam (e-beam) radiation, a form of ionizing energy, is generally

characterized by low penetration and high-dose rates. E-beam irradiation is

similar to gamma radiation in that it alters various chemical and molecular

bonds on contact. Beams produced for e-beam sterilization are concentrated,

highly-charged streams of electrons.

E-beams are for sterilization of items ranging from syringes to

cardiothoracic devices.


4/6

C-STERILIZATION BY FILTRATIONFiltrationinvolves the physical removal (exclusion) of all cells in a liquid

or gas. It is especially important for sterilization of solutions which would be

denatured by heat (e.g. antibiotics, injectable drugs, amino acids, vitamins,

etc.). Portable units can be used in the field for water purification and

industrial units can be used to "pasteurize" beverages. Essentially, solutions

or gases are passed through a filter of sufficient pore diameter (generally

0.22 micron) to remove the smallest known bacterial cells.

Advantages:1- removes rather than destroys microorganisms i.e. both living and dead

cells are removed

2- does not affect the physical or chemical integrity of the sterilized material3- have an important role in sterility testingDisadvantages:

1-bacterial toxins are not removed2- requires highly trained staffTypes:

1- Depth filters:made of sintered glass or ceramic (granular) or asbestos orcellulosic fibers (fibrous). Retains or traps MO within the filter matrix.

2- Screen filters: either membranous (thin film of cellulose ester) ornucleopore (thin film of plastic). Retain MO on the surface.


5/6

A typical set-up in a microbiology laboratory for filtration sterilization of medium

components that would be denatured or changed by heat sterilization. The filter is placed

(aseptically) on the glass platform, then the funnel is clamped and the fluid is drawn by

vacuum into a previously sterilized flask. The recommended size filter that will exclude

the smallest bacterial cells is 0.22 micron.

STERILIZATION OF AIR

Sterile air (less than 2 colonies/cubic feet) is required for:

1- Aseptic area for aseptic filling of sterile pharmaceuticals2- Biotechnology in fermentation processesMethods of air sterilization:

1- Treatment with chemicals: by spraying of gases or fluids such asformaldehyde or lactic acid


6/6

2- UV irradiation: used mainly to maintain sterility of air or reduce the levelof contamination in hospitals

3- Filtration: used for sterilization with efficiency 99.9%. Depends on theuse of several types of filters:

a- Cotton or glass wool fibrous pads filtersb- Cellulose paper filtersc- Cartridge multitube membrane filterd- High efficiency particulate air (HEPA) filters

ASEPTIC AREA

Special room or area having the following features:

1- Kept under slight positive pressure2- Smooth walls, ceiling and floor to prevent accumulation of particles3- Windows are double glass4- Doors are double with air lock5- Sterile air supply6- UV irradiation when out of work7- Persons should be free from infection and must wear sterile clothes8- Air must be routinely analyzed9- Entry should be through the following sequence:

- black area: non sterile- gray area: intermediate for washing and changing- white area: aseptic area

MICROBIAL ANALYSIS OF AIR

1- Settling plates: Petri dishes with agar left open and then incubated andcolonies are counted. This method is slow and not very accurate.

2- Agar impinges: by the use of air sampler, where controlled volume of airis forced to pass through a slit, below which a revolving small nutrient

agar plate is placed.

Microsoft Word - Cold Sterilization Unidad 4

Documents

Transcript of Microsoft Word - Cold Sterilization Unidad 4