Sterilization (microbiology)

Sterilization (British English: sterilisation) refers to any process that removes, kills, or deactivates all forms of life (particularly microorganisms such as fungi, bacteria, spores, and unicellular eukaryotic organisms) and other biological agents (such as prions or viruses) present in fluid or on a specific surface or object.

Sterilization is distinct from disinfection, sanitization, and pasteurization, in that those methods reduce rather than eliminate all forms of life and biological agents present.

[citation needed] For high-risk applications, such as medical devices and injections, a sterility assurance level of at least 10−6 is required by the United States of America Food and Drug Administration (FDA).

The object or liquid is placed in the autoclave chamber, which is then sealed and heated using pressurized steam to a temperature set point for a defined period of time.

Gravity displacement cycles rely on the lower density of the injected steam to force cooler, denser air out of the chamber drain.

Steam Sterilization | Disinfection & Sterilization Guidelines | Guidelines Library | Infection Control | CDC In comparison, pre-vacuum cycles create a vacuum in the chamber to remove cool dry air prior to injecting saturated steam, resulting in faster heating and shorter cycle times.

This may be achieved by gradually depressurizing the sterilization chamber and allowing liquids to evaporate under a negative pressure, while cooling the contents.

Using mice as test animals, one experiment showed that heating BSE positive brain tissue at 134–138 °C (273–280 °F) for 18 minutes resulted in only a 2.5 log decrease in prion infectivity.

[18][failed verification] To sterilize waste materials that are chiefly composed of liquid, a purpose-built effluent decontamination system can be utilized.

Forced ventilation of hot air can be used to increase the rate at which heat is transferred to an organism and reduce the temperature and amount of time needed to achieve sterility.

[20][21] Dry heat has the advantage that it can be used on powders and other heat-stable items that are adversely affected by steam (e.g., it does not cause rusting of steel objects).

Therefore, special heaters have been developed that surround the inoculating loop with a heated cage, ensuring that such sprayed material does not further contaminate the area.

[citation needed] 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.

[35] Nitrogen dioxide (NO2) gas is a rapid and effective sterilant for use against a wide range of microorganisms, including common bacteria, viruses, and spores.

The unique physical properties of NO2 gas allow for sterilant dispersion in an enclosed environment at room temperature and atmospheric pressure.

The mechanism for lethality is the degradation of DNA in the spore's core through nitration of the phosphate backbone, which kills the exposed organism as it absorbs NO2.

[36] NO2 has a boiling point of 21 °C (70 °F) at sea level, which results in a relatively high saturated vapour pressure at ambient temperature.

Additionally, the low levels of concentration required, coupled with the high vapour pressure, assures that no condensation occurs on the devices being sterilized.

Noxilizer, Inc. has commercialized this technology to offer contract sterilization services for medical devices at its Baltimore, Maryland (USA) facility.

Glutaraldehyde and formaldehyde solutions (also used as fixatives) are accepted liquid sterilizing agents, provided that the immersion time is sufficiently long.

[44] Drawbacks of hydrogen peroxide include material compatibility, a lower capability for penetration and operator health risks.

[45] The penetrating ability of hydrogen peroxide is not as good as ethylene oxide[citation needed] and so there are limitations on the length and diameter of the lumen of objects that can be effectively sterilized.

[48][49] Vaporized hydrogen peroxide (VHP) is used to sterilize large enclosed and sealed areas, such as entire rooms and aircraft interiors.

[56] Sterilization can be achieved using electromagnetic radiation, such as ultraviolet light (UV), X-rays, and gamma rays, or irradiation by subatomic particles such as electron beams.

Gamma radiation is very penetrating, and is commonly used for sterilization of disposable medical equipment, such as syringes, needles, cannulas and IV sets, and food.

Other uncommonly used designs are dry storage, providing movable shields that reduce radiation levels in areas of the irradiation chamber, etc.

An incident in Decatur, Georgia, USA, where water-soluble caesium-137 leaked into the source storage pool, required Nuclear Regulatory Commission (NRC) intervention[59] and led to the use of this radioisotope being almost entirely discontinued in favor of the more costly, non-water-soluble cobalt-60.

[60] High-energy X-rays (produced by bremsstrahlung) allow irradiation of large packages and pallet loads of medical devices.

X-rays are generated by bombarding a dense material (target) such as tantalum or tungsten with high-energy electrons, in a process known as bremsstrahlung conversion.

Membrane filters used in production processes are commonly made from materials such as mixed cellulose ester or polyethersulfone (PES).