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维基百科关于消毒与灭菌的词条.
Disinfectant Disinfection of a floor using a mopDisinfectants are antimicrobial agents that are applied to non-living objects to destroy microorganisms, the process of which is known as disinfection. Disinfectants should generally be distinguished from antibiotics that destroy microorganisms within the body, and from antiseptics, which destroy microorganisms on living tissue. Sanitisers are high level disinfectants that kill over 99.9% of a target microorganism in applicable situations. Very few disinfectants and sanitisers can sterilise (the complete elimination of all microorganisms), and those that can depend entirely on their mode of application. Bacterial endospores are most resistant to disinfectants, however some viruses and bacteria also possess some tolerance.
Contents
1 Properties
2 Types of disinfectants
2.1 Alcohols
2.2 Aldehydes
2.3 Halogens
2.4 Oxidizing agents
2.5 Phenolics
2.6 Quaternary ammonium compounds
2.7 Other
3 Relative effectiveness of disinfectants
4 Home disinfectants
5 References
6 See also
7 External links
Properties
A perfect disinfectant would offer complete sterilisation, without harming other forms of life, be inexpensive, and non-corrosive. Unfortunately ideal disinfectants do not exist. All disinfectants are also, by their very nature, potentially harmful (even toxic) to humans or animals. They should be treated with appropriate care. Most come with safety instructions printed on the packaging, which should be read in full before using the disinfectant. Most modern household disinfectants contain Bitrex, an exceptionally bitter substance designed to discourage ingestion, as an added safety measure. Those that are used indoors should never be mixed with other cleaning products as chemical reactions can occur. They are frequently used in hospitals, dental surgeries, kitchens and bathrooms to kill infectious organisms.
The choice of the disinfectant to be used depends on the particular situation. Some disinfectants have a wide spectrum (kill nearly all microorganisms), whilst others kill a smaller range of disease-causing organisms but are preferred for other properties (they may be non-corrosive, non-toxic, or inexpensive).
The disinfecting properties of sunlight (ultra-violet) are powerful. Rather than total reliance on chemicals, basic hygiene - a pillar of food safety - is important in the fight against bacteria since they generally prefer a warm-moist-dark environment. There are arguments for creating or maintaining conditions which are not conducive to bacterial survival and multiplication, rather than attempting to kill them with chemicals. Bacteria have a very rapid multiplication rate, which enables them to evolve rapidly. Should some bacteria survive a chemical attack, they give rise to the next generation. Thus they are able to develop resistance to hostile chemicals. For this reason, some question the wisdom of impregnating cloths, cutting boards and worktops in the home with bactericidal chemicals. Hygiene is important in prevention of foodborne illness.
Types of disinfectants
Disinfection liquid attached to hospital bed
Alcohols
Alcohols, usually ethanol or isopropanol, are wiped over benches and skin and allowed to evaporate for quick disinfection. They have wide microbiocidal activity, are non corrosive, but can be a fire hazard. They also have limited residual activity due to evaporation, and have a limited activity in the presence of organic material. Alcohols are more effective combined with water—70% isopropyl alcohol or 62% ethyl alcohol is more effective than 95% alcohol. Alcohol is not effective against fungal or bacterial spores.
Aldehydes
Aldehydes, such as Glutaraldehyde, have a wide microbiocidal activity and are sporocidal and fungicidal. They are partly inactivated by organic matter and have slight residual activity.
Halogens
Chloramine is used in drinking water treatment instead of chlorine because it produces fewer disinfection byproducts.
Chlorine is used to disinfect swimming pools, and is added in small quantities to drinking water to reduce waterborne diseases.
Hypochlorites (Sodium hypochlorite), often in the form of common household bleach, are used in the home to disinfect drains, and toilets. Other hypochlorites such as calcium hypochlorite are also used, especially as a swimming pool additive. Hypochlorites yield an aqueous solution of hypochlorous acid that is the true disinfectant. Hypobromite solutions are also sometimes used.
Iodine is usually dissolved in an organic solvent or as Lugol's iodine solution. It is used in the poultry industry. It is added to the birds' drinking water. Although no longer recommended because it increases scar tissue formation and increases healing time, tincture of iodine has also been used as an antiseptic for skin cuts and scrapes.
Oxidizing agents
Oxidizing agents act by oxidising the cell membrane of microorganisms, which results in a loss of structure and leads to cell lysis and death.
Chlorine dioxide is used as an advanced disinfectant for drinking water to reduce waterborne diseases. In certain parts of the world, it has largely replaced chlorine because it forms fewer byproducts. Sodium chlorite, sodium chlorate, and potassium chlorate are used as precursors for generating chlorine dioxide.
Hydrogen peroxide is used in hospitals to disinfect surfaces. It is sometimes mixed with colloidal silver. It is often preferred because it causes far fewer allergic reactions than alternative disinfectants. Also used in the food packaging industry to disinfect foil containers. A 3% solution is also used as an antiseptic. When hydrogen peroxide comes into contact with the catalase enzyme in cells it is broken down into water and a hydroxyl free radical. It is the damage caused by the oxygen free radical that kills bacteria. However, recent studies have shown hydrogen peroxide to be toxic to growing cells as well as bacteria; its use as an antiseptic is no longer recommended.[citation needed]
Ozone is a gas that can be added to water for sanitation.
Acidic Electrolyzed Water is a strong oxidising solution made from the electrolysis of ordinary tap water in the presence of a specific amount of salt, generally sodium chloride. Anolyte has a typical pH range of 3.5 to 8.5 and an Oxidation-Reduction Potential (ORP) of +600 to +1200 mV. The most powerful anolyte disinfecting solution is that produced at a controlled 5.0 to 6.3 pH where the predominant oxchlorine species is hypochlorous acid. This environmentally-responsible disinfectant is highly efficacious against bacteria, fungus, mold, spores and other micro-organisms, in very short contact times. It may be applied as liquid, fog or ice.
Peracetic acid is a disinfectant produced by reacting hydrogen peroxide with acetic acid. It is broadly effective against microorganisms and is not deactivated by catalase and peroxidase, the enzymes which break down hydrogen peroxide. It also breaks down to food safe and environmentally friendly residues (acetic acid and hydrogen peroxide), and therefore can be used in non-rinse applications. It can be used over a wide temperature range (0-40°C), wide pH range (3.0-7.5), in clean-in-place (CIP) processes, in hard water conditions, and is not affected by protein residues.
Potassium permanganate (KMnO4) is a red crystalline powder that colours everything it touches, and is used to disinfect aquariums. It is also used widely in community swimming pools to disinfect ones feet before entering the pool. Typically, a large shallow basin of KMnO4/water solution is kept near the pool ladder. Participants are required to step in the basin and then go into the pool. Additionally, it is widely used to disinfect community water ponds and wells in tropical countries, as well as to disinfect the mouth before pulling out teeth. It can be applied to wounds in dilute solution; potassium permanganate is a very useful disinfectant.
Potassium peroxymonosulfate, the principal ingredient in Virkon, is a wide-spectrum disinfectant used in labs. Virkon kills bacteria, viruses, and fungi. It is used as a 1% solution in water, and keeps for one week once it is made up. It is expensive, but very effective, its pink colour fades as it is used up so it is possible to see at a glance if it is still fresh.
Phenolics
Phenolics are active ingredients in some household disinfectants. They are also found in some mouthwashes and in disinfectant soap and handwashes.
Phenol is probably the oldest known disinfectant as it was first used by Lister, when it was called carbolic acid. It is rather corrosive to the skin and sometimes toxic to sensitive people.
O-phenylphenol is often used instead of Phenol, since it is somewhat less corrosive.
Chloroxylenol is the principal ingredient in Dettol, a household disinfectant and antiseptic.
Hexachlorophene is a phenolic that was once used as a germicidal additive to some household products but was banned due to suspected harmful effects.
Thymol, derived from the herb thyme, is the active ingredient in the only 100% botanical disinfectant with an EPA registration (#74771-1), Benefect. Registered as "broad spectrum," or hospital-grade, it is also the only disinfectant with a green certification, Environmental Choice.
Quaternary ammonium compounds
Quaternary ammonium compounds (Quats), such as benzalkonium chloride, are a large group of related compounds. Some have been used as low level disinfectants. They are effective against bacteria, but not against some species of Pseudomonas bacteria or bacterial spores. Quats are biocides which also kill algae and are used as an additive in large-scale industrial water systems to minimize undesired biological growth. Quaternary ammonium compounds can also be effective disinfectants against enveloped viruses.
Other
High-intensity shortwave ultraviolet light can be used for disinfecting smooth surfaces such as dental tools, but not porous materials that are opaque to the light such as wood or foam. Ultraviolet light fixtures are often present in microbiology labs, and are activated only when there are no occupants in a room (e.g., at night).
Relative effectiveness of disinfectants
One way to compare disinfectants is to compare how well they do against a known disinfectant and rate them accordingly. Phenol is the standard, and the corresponding rating system is called the "Phenol coefficient". The disinfectant to be tested is compared with phenol on a standard microbe (usually Salmonella typhi or Staphylococcus aureus). Disinfectants that are more effective than phenol have a coefficient > 1. Those that are less effective have a coefficient < 1.
Home disinfectants
By far the most cost-effective home disinfectant is the commonly used chlorine bleach (a 5% solution of Sodium hypochlorite) which is effective against most common pathogens, including such difficult organisms tuberculosis (mycobacterium tuberculosis), hepatitis B and C, fungi, and antibiotic-resistant strains of staphylococcus and enterococcus. It even has some disinfectant action against parasitic organisms [1]. Positives are that it kills the widest range of pathogens of any inexpensive disinfectant; it is extremely powerful against viruses and bacteria at room temperature; it is commonly available and inexpensive; and it breaks down quickly into harmless components (primarily table salt and oxygen). Negatives are that it is caustic to the skin and eyes, especially at higher concentrations; like many common disinfectants, it degrades in the presence of organic substances; it smells bad; it is not effective against giardia lamblia and cryptosporidium; and extreme caution must be taken not to combine it with ammonia or any acid (such as vinegar). The best practice is not to add anything to household bleach except water. Dilute bleach can be tolerated on the skin for a period of time by most persons, as witnessed by the long exposure to extremely dilute "chlorine" (actually sodium or calcium hypochlorite) many children get in swimming pools.
To use chlorine bleach effectively, the surface or item to be disinfected must be clean. In the bathroom, special caution must be taken to wipe up urine. A 1 to 20 solution in water is effective simply by being wiped on and left to dry. The user should wear rubber gloves and, in tight airless spaces, goggles. If parasitic organisms are suspected, it should be applied at 1 to 1 concentration, or even undiluted; extreme caution must be taken to avoid contact with eyes and mucous membranes. Protective goggles and good ventilation are mandatory when applying concentrated bleach.
Where one does not want to risk the corrosive effects of bleach, alcohol-based disinfectants are reasonably inexpensive and quite safe. The great drawback to them is their rapid evaporation; sometimes effective disinfection can be obtained only by immersing an object in the alcohol.
References
^ EPA's Registered Sterilizers, Tuberculocides, and Antimicrobial Products Against HIV-1, and Hepatitis B and Hepatitis C Viruses. (Obtained January 4, 2006)
Sterilization (microbiology)
Sterilization (or sterilisation) refers to any process that effectively kills or eliminates transmissible agents (such as fungi, bacteria, viruses and prions) from a surface, equipment, foods, medications, or biological culture medium. Sterilization can be achieved through application of heat, chemicals, irradiation, or filtration.
Contents
1 Applications
1.1 Foods
1.2 Medicine and Surgery
2 Heat sterilization
2.1 Steam Sterilization
2.2 Food
2.3 Food Utensils
2.4 Bathing
2.5 Other Methods
3 Chemical sterilization
4 Radiation sterilization
5 Sterile filtration
6 References
7 External links
Applications
Foods
The first application of sterilization was thorough cooking to effect the partial heat sterilization of foods and water. Cultures that practice heat sterilization of food and water have longer life expectancy and lower rates of disability. Canning of foods by heat sterilization was an extension of the same principle. Ingestion of contaminated food and water remains a leading cause of illness and death in the developing world, particularly for children.
Medicine and Surgery
In general, surgical instruments and medications that enter an already sterile part of the body (such as the blood, or beneath the skin) must have a high sterility assurance level. Examples of such instruments include scalpels, hypodermic needles and artificial pacemakers. This is also essential in the manufacture of parenteral pharmaceuticals.
Heat sterilization of medical instruments is known to have been used in Ancient Rome, but it mostly disappeared throughout the Middle Ages resulting in significant increases in disability and death following surgical procedures.
Preparation of injectable medications and intravenous solutions for fluid replacement therapy requires not only a high sterility assurance level, but well-designed containers to prevent entry of adventitious agents after initial sterilization.
Heat sterilization
Steam Sterilization
Front-loading autoclaves are very common.A widely-used method for heat sterilization is the autoclave. Autoclaves commonly use steam heated to 121°C (250°F), at 103 kPa (15 psi) above atmospheric pressure. Solid surfaces are effectively sterilized when heated this temperature for at least 15 minutes or to 134°C for a minimum of 3 minutes. However, liquids and instruments packed in layers of cloth require a much longer time to reach a sterilizing temperature. After sterilization, autoclaved liquids must be cooled slowly to avoid boiling over when the pressure is released.
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 scrapie (strain 263K) is inactivated relatively quickly by such sterilization procedures; however, other strains of scrapie, as well as strains of CJD and BSE are more resistant. 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. (The initial BSE concentration in the tissue was relatively low). For a significant margin of safety, cleaning should reduce infectivity by 4 logs, and the sterilization method should reduce it a further 5 logs.
To ensure the autoclaving process was able to cause sterilization, most autoclaves have meters and charts that record or display pertinent information such as temperature and pressure as a function of time. Indicator tape is often placed on packages of products prior to autoclaving. A chemical in the tape will change color when the appropriate conditions have been met. Some types of packaging have built-in indicators on them.
Biological indicators ("bioindicators") can also be used to independently confirm autoclave performance. Simple bioindicator devices are commercially available based on microbial spores. Most contain spores of the heat resistant microbe Bacillus stearothermophilus, among the toughest organisms for an autoclave to destroy. Typically these devices have a self-contained liquid growth medium and a growth indicator. During autoclaving an internal glass ampule is shattered, releasing the spores into the growth medium. The vial is then incubated (typically at at 56°C (132°F)) for 48 hours. If the autoclave destroyed the spores, the medium will remain its original color. If autoclaving was unsuccessful the B. sterothermophilus will metabolize during incubation, causing a color change during the incubation.
For effective sterilization, steam needs to penetrate the autoclave load uniformly, so an autoclave must not be overcrowded, and the lids of bottles and containers must be left ajar. During the initial heating of the chamber, residual air must be allowed to escape as steam enters the autoclave chamber; otherwise the final temperature will be less than that of the entering steam. Indicators should be placed in the most difficult places for the steam to reach to ensure that steam actually penetrates there.
For autoclaving, as for all disinfection of sterilization methods, cleaning is critical. Extraneous biological matter or grime may shield organisms from the property intended to kill them, whether it physical or chemical. Cleaning can also remove a large number of organisms. Proper cleaning can be achieved by physical scrubbing. This should be done with detergent and warm water to get the best results. Cleaning instruments or utensils with organic matter, cool water must be used because warm or hot water may cause organic debris to coagulate. Treatment with ultrasound or pulsed air can also be used to remove debris.
Food
Although imperfect, cooking and canning are the most common applications of heat sterilization. Boiling water kills the vegetative stage of all common microbes. Roasting meat until it is well done typically completely sterilizes the surface. Since the surface is also the part of food most likely to be contaminated by microbes, roasting usually prevents food poisoning. Note that the common methods of cooking food do not sterilize food - they simply reduce the number of disease-causing micro-organisms to a level that is not dangerous for people with normal digestive and immune systems. Pressure cooking is analogous to autoclaving and when performed correctly renders food sterile. However, some foods are notoriously difficult to sterilize with home canning equipment, so expert recommendations should be followed for home processing to avoid food poisoning.
See also Food safety.
Food Utensils
Dishwashers often only use hot tap water or heat the water to between 49 and 60°C (120 and 140°F), and thus provide temperatures that could promote bacterial growth. That is to say, they do not effectively sterilize utensils. Some dishwashers do actually heat water up to 74°C (165°F) or higher; those often are specifically described as having sterilization modes of some sort, but this is not a substitute for autoclaving. Note that dishwashers remove food traces from the utensils by a combination of mechanical action (the action of water hitting the plates and cutlery) and the action of detergents and enzymes on fats and proteins. This removal of food particles thus removes one of the factors required for bacterial growth (food), and explains why items with cracks and crevices should either be washed by hand or disposed of: if the water cannot get to the area needing cleaning, the warm, moist, dark conditions in the dishwasher can actually promote bacterial growth.
Bathing
Bathing and washing are not hot enough to sterilize bacteria without scalding the skin. Most hot tap water is between 43 and 49°C (110 and 120°F), though some people set theirs as high as 55°C (130°F). Humans begin to find water painful at 41 to 42°C (106 to 108°F), which to many bacteria is just starting to get warm enough for them to grow quickly; they will grow faster, rather than be killed at temperatures up to 55°C (130°F) or more.
Other Methods
Other heat methods include flaming, incineration, boiling, tindalization, and using dry heat.
Flaming is done to loops and straight-wires in microbiology labs. Leaving the loop in the flame of a Bunsen burner or alcohol lamp until it glows red ensures that any infectious agent gets inactivated. This is commonly used for small metal or glass objects, but not for large objects (see Incineration below). However, during the initial heating infectious material may be "sprayed" from the wire surface before it is killed, contaminating nearby surfaces and objects. Therefore, special heaters have been developed that surround the innoculating loop with a heated cage, ensuring that such sprayed material does not further contaminate the area.
Incineration will also burn any organism to ash. It is used to sanitize medical and other biohazardous waste before it is discarded with non-hazardous waste.
Boiling in water for 15 minutes will kill most vegetative bacteria and viruses, but boiling is ineffective against prions and many bacterial and fungal spores; therefore boiling is unsuitable for sterilization. However, since boiling does kill most vegetative microbes and viruses, it is useful for reducing viable levels if no better method is available. Boiling is a simple process, and is an option available to most anyone most anywhere, requiring only water, enough heat, and a container that can withstand the heat; however, boiling can be hazardous and cumbersome.
Tindalization[1] /Tyndallization[2] named after John Tyndall is a lengthy 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, boiling, cooling, incubating for a day, boiling, cooling, incubating for a day, and finally boiling again. The three 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. This is effective because many spores are stimulated to grow by the heat shock. The procedure only works for media that can support bacterial growth - it will not sterilize plain water. Tindalization/tyndallization is ineffective against prions.
Dry heat can be used to sterilize items, but as the heat takes much longer to be transferred to the organism, both the time and the temperature must usually be increased, unless forced ventilation of the hot air is used. The standard setting for a hot air oven is at least two hours at 160°C (320°F). A rapid method heats air to 190°C (374°F) for 6 minutes for unwrapped objects and 12 minutes for wrapped objects [1] [2]. Dry heat has the advantage that it can be used on powders and other heat-stable items that are adversely affected by steam (for instance, it does not cause rusting of steel objects).
Prions can be inactivated by immersion in sodium hydroxide (NaOH 0.09N) for two hours plus one hour autoclaving (121°C / 250°F). Several investigators have shown complete (>7.4 logs) inactivation with this combined treatement. However, sodium hydroxide may corrode surgical instruments, especially at the elevated temperatures of the autoclave.
Chemical sterilization
Chemicals are also used for sterilization. Although heating provides the most reliable way to rid objects of all transmissible agents, it is not always appropriate, because it will damage heat-sensitive materials such as biological materials, fiber optics, electronics, and many plastics.
Ethylene oxide (EO or EtO) gas is commonly used to sterilize objects sensitive to temperatures greater than 60°C such as plastics, optics and electrics. Ethylene oxide treatment is generally carried out between 30°C and 60°C with relative humidity above 30% and a gas concentration between 200 - 800 mg/L for at least three hours. Ethylene oxide penetrates well, moving through paper, cloth, and some plastic films and is highly effective. Ethylene oxide sterilizers are used to process sensitive instruments which cannot be adequately sterilized by other methods. EtO can kill all known viruses, bacteria and fungi, including bacterial spores and is satisfactory for most medical materials, even with repeated use. However it is highly flammable, and requires a longer time to sterilize than any heat treatment. The process also requires a period of post-sterilization aeration to remove toxic residues. Ethylene oxide is the most common sterilization method, used for over 70% of total sterilizations, and for 50% of all disposable medical devices.
The two most important ethylene oxide sterilization methods are: (1) the gas chamber method and (2) the micro-dose method. To benefit from economies of scale, EtO has traditionally been delivered by flooding a large chamber with a combination of EtO and other gases used as dilutants (usually CFCs or carbon dioxide ). This method has drawbacks inherent to the use of large amounts of sterilant being released into a large space, including air contamination produced by CFCs and/or large amounts of EtO residuals, flammability and storage issues calling for special handling and storage, operator exposure risk and training costs. Because of these problems a micro-dose sterilization method was developed in the late 1950's, using a specially designed bag to eliminate the need to flood a larger chamber with EtO. This method is also known as gas diffusion sterilization, or bag sterilization. This method minimize the use of gas.[3]
Bacillus subtilis, a very resistant organism, is used as a rapid biological indicator for EO sterilizers. If sterilization fails, incubation at 37°C causes a fluorescent change within four hours, which is read by an auto-reader. After 96 hours, a visible color change occurs. Fluorescence is emitted if a particular (EO resistant) enzyme is present, which means that spores are still active. The color change indicates a pH shift due to bacterial metabolism. The rapid results mean that the objects treated can be quarantined until the test results are available.
Ozone is used in industrial settings to sterilize water and air, as well as a disinfectant for surfaces. It has the benefit of being able to oxidize most organic matter. On the other hand, it is a toxic and unstable gas that must be produced on-site, so it is not practical to use in many settings.
Chlorine bleach is another accepted liquid sterilizing agent. Household bleach consists of 5.25% sodium hypochlorite. It is usually diluted to 1/10 immediately before use; however to kill Mycobacterium tuberculosis it should be diluted only 1/5. The dilution factor must take into account the volume of any liquid waste that it is being used to sterilize.[4] Bleach will kill many organisms immediately, but for full sterilization it should be allowed to react for 20 minutes. Bleach will kill many, but not all spores. It is highly corrosive and may corrode even stainless steel surgical instruments.
Glutaraldehyde and formaldehyde solutions (also used as fixatives) are accepted liquid sterilizing agents, provided that the immersion time is sufficiently long. To kill all spores in a clear liquid can take up to 12 hours with glutaraldehyde and even longer with formaldehyde. The presence of solid particles may lenghthen the required period or render the treatment ineffective. Sterilization of blocks of tissue can take much longer, due to the time required for the fixative to penetrate. Glutaraldehyde and formaldehyde are volatile, and toxic by both skin contact and inhalation. Glutaraldehyde has a short shelf life (<2 weeks), and is expensive. Formaldehyde is less expensive and has a much longer shelf life if some methanol is added to inhibit polymerization to paraformaldehyde, but is much more volatile. Formaldehyde is also used as a gaseous sterilizing agent; in this case, it is prepared on-site by depolymerization of solid paraformaldehyde. Many vaccines, such as the original Salk polio vaccine, are sterilized with formaldehyde.
Ortho-phthalaldehyde (OPA) is a chemical sterilizing agent that received Food and Drug Administration (FDA) clearance in late 1999. Typically used in a 0.55% solution, OPA shows better myco-bactericidal activity than glutaraldehyde. It also is effective against glutaraldehyde-resistant spores. OPA has superior stability, is less volatile, and does not irritate skin or eyes, and it acts more quickly than glutaraldehyde. On the other hand, it is more expensive, and will stain proteins (including skin) gray in color.
Hydrogen peroxide is another chemical sterilizing agent. It is relatively non-toxic once diluted to low concentrations (although a dangerous oxidizer at high concentrations), and leaves no residue.
Sterrad sterilization chambers use hydrogen peroxide vapor to sterilize heat-sensitive equipment such as rigid endoscopes. A recent model can sterilize most hospital loads in as little as 20 minutes. The Sterrad has limitations with processing certain materials such as paper/linens and long thin lumens. Paper products cannot be sterilized in the Sterrad system because of a process called cellulostics, in which the hydrogen peroxide would be completely absorbed by the paper product.
Hydrogen peroxide and formic acid are mixed as needed in the Endoclens device for sterilization of endoscopes. This device has two independent asynchronous bays, and cleans (in warm detergent with pulsed air), sterilizes and dries endoscopes automatically in 30 minutes. Studies with synthetic soil with bacterial spores showed the effectiveness of this device.
Dry Sterilization Process (DSP) uses hydrogen peroxide at a concentration of 30-35% under low pressure conditions. This process achieves bacterial reduction of 10-6...10-8. The complete process cycle time is just 6 seconds, and the surface temperature is increased only 10°-15°C. Originally designed for the sterilization of plastic bottles in the beverage industry, because of the high germ reduction and the slight temperature increase the Dry Sterilization Process is also useful for medical and pharmaceutical applications.
Peracetic acid (0.2%) is used to sterilize instruments in the Steris system.
Prions are highly resistant to chemical sterilization. Treatment with aldehydes (e.g., formaldehyde) have actually been shown to increase prion resistance. Hydrogen peroxide (3%) for one hour was shown to be ineffective, providing less than 3 logs (10-3) reduction in contamination. Iodine, formaldehyde, glutaraldehyde and peracetic acid also fail this test (one hour treatment). Only chlorine, a phenolic compound, guanidinium thiocyanate, and sodium hydroxide (NaOH) reduce prion levels by more than 4 logs. Chlorine and NaOH are the most consistent agents for prions. Chlorine is too corrosive to use on certain objects. Sodium hydroxide has had many studies showing its effectiveness.
Radiation sterilization
Methods exist to sterilize using radiation such as X-rays, gamma rays, or subatomic particles.
Gamma rays are very penetrating and are commonly used for sterilization of disposable medical equipment, such as syringes, needles, canulas and IV sets. Gamma radiation requires bulky shielding for the safety of the operators; they also require storage of a radioisotope (usually Cobalt-60), which continuously emits gamma rays (it cannot be turned off, and therefore always presents a hazard in the area of the facility).
X-rays are less penetrating than gamma rays and tend to require longer exposure times, but require less shielding, and are generated by an X-ray machine that can be turned off for servicing and when not in use.
Ultraviolet light irradiation (UV, from a germicidal lamp) is useful only for sterilization of surfaces and some transparent objects. Many objects that are transparent to visible light absorb UV. UV irradiation is routinely used to sterilize the interiors of biological safety cabinets between uses, but is ineffective in shaded areas, including areas under dirt (which may become polymerized after prolonged irradiation, so that it is very difficult to remove). It also damages many plastics, such as polystyrene foam.
Further information: Ultraviolet Germicidal Irradiation
Subatomic particles may be more or less penetrating, and may be generated by a radioisotope or a device, depending upon the type of particle.
Irradiation with X-rays or gamma rays does not make materials radioactive. Irradiation with particles may make materials radioactive, depending upon the type of particles and their energy, and the type of target material: neutrons and very high-energy particles can make materials radioactive, but have good penetration, whereas lower energy particles (other than neutrons) cannot make materials radioactive, but have poorer penetration.
Irradiation is used by the United States Postal Service to sterilize mail in the Washington, DC area. Some foods (e.g. spices, ground meats) are irradiated for sterilization (see food irradiation).
Sterile filtration
Clear liquids that would be damaged by heat, irradiation or chemical sterilization can be sterilized by mechanical filtration. This method is commonly used for sensitive pharmaceuticals and protein solutions in biological research. A filter with pore size 0.2 µm will effectively remove bacteria. If viruses must also be removed, a much smaller pore size around 20 nm is needed. Solutions filter slowly through membranes with smaller pore diameters. Prions are not removed by filtration. The filtration equipment and the filters themselves may be purchased as presterilized disposable units in sealed packaging, or must be sterilized by the user, generally by autoclaving at a temperature that does not damage the fragile filter membranes. To ensure sterility, the filtration system must be tested to ensure that the membranes have not been punctured prior to or during use.
One may also use a "flowbox", a device which produces a laminar stream of air flowing downwards, kept at constant temperature by special air conditioning. It is particullary important when working with pure cultures.
References
Central Service Technical Manual, 6th Edition, Jack Ninemeier, PhD, Editor , International Association of Healthcare Central Service Materiel Management
Control of microbes
^ Mesquita, J. A. M.; Teixeira, M.A. and Brandao, S. C. C. (1998). "Tindalization of goats' milk in glass bottles.". J. Anim. Sci. /J. Dairy Sci. Vol. 76, Suppl. 1 / Vol. 81, Suppl. 1/: 21. Retrieved on 2007-03-06.
^ Thiel, Theresa (1999). http://www.umsl.edu/~microbes/pdf/tyndallization.pdf (pdf). Science in the Real World. Retrieved on 2007-03-06.
^ Micro-dose sterilization method
^ Beth Israel Deaconess Medical Center Biosafety Manual (2004 edition)
Raju, G.K. & Cooney, C.L., 1993. Media and air sterilization. in Biotechnology, ed. Stephanopoulos, G., Vol 3., pp 157-184. |
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