Sterilization (or sterilisation) is a term referring to any process that eliminates (removes) or kills all forms of and other (such as, as well as which some do not consider to be but are nonetheless), including transmissible agents (such as, spore forms, organisms such as, etc.) present in a specified region, such as a surface, a volume of fluid, medication, or in a compound such as biological. Sterilization can be achieved with one or more of the following:,.
Sterilization is distinct from, sanitization, and in that sterilization kills, deactivates, or eliminates all forms of life and other biological agents. Contents.Applications FoodsOne of the first steps toward sterilization was made by who discovered that thorough application of heat over a suitable period slowed the decay of foods and various liquids, preserving them for safe consumption for a longer time than was typical.
Of foods is an extension of the same principle, and has helped to reduce ('food poisoning'). Other methods of sterilizing foods include and high pressure. Medicine and surgery. Front-loading autoclaveA widely used method for heat sterilization is the autoclave, sometimes called a converter or steam sterilizer. Autoclaves use steam heated to 121-134 °C under pressure. To achieve sterility, the article is heated in a chamber by injected steam until the article reaches a time and temperature setpoint. The article is then held at that setpoint for a period of time which varies depending on the present on the article being sterilized and its resistance (D-value) to steam sterilization.
A general cycle would be anywhere between 3 and 15 minutes, (depending on the generated heat) at 121 °C at 100 kPa, which is sufficient to provide a sterility assurance level of 10 −4 for a product with a bioburden of 10 6 and a D-value of 2.0 minutes. Following sterilization, liquids in a pressurized autoclave must be cooled slowly to avoid boiling over when the pressure is released. This may be achieved by gradually depressurizing the sterilization chamber and allowing liquids to evaporate under a negative pressure, while cooling the contents.Proper autoclave treatment will inactivate all resistant bacterial in addition to, bacteria, and viruses, but is not expected to eliminate all, which vary in their resistance. For prion elimination, various recommendations state 121-132 °C for 60 minutes or 134 °C for at least 18 minutes. The 263K prion is inactivated relatively quickly by such sterilization procedures; however, other strains of scrapie, and strains of and are more resistant.
Using as test animals, one experiment showed that heating BSE positive tissue at 134-138 °C for 18 minutes resulted in only a 2.5 decrease in prion infectivity. Most autoclaves have meters and charts that record or display information, particularly temperature and pressure as a function of time. The information is checked to ensure that the conditions required for sterilization have been met. Indicator tape is often placed on packages of products prior to autoclaving, and some packaging incorporates indicators.
The indicator changes color when exposed to steam, providing a visual confirmation.Biological indicators 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 (formerly Bacillus stearothermophilus), which is extremely resistant to steam sterilization. Biological indicators may take the form of glass vials of spores and liquid media, or as spores on strips of paper inside envelopes.
These indicators are placed in locations where it is difficult for steam to reach to verify that steam is penetrating there.For autoclaving, cleaning is critical. Extraneous biological matter or grime may shield organisms from steam penetration. Proper cleaning can be achieved through physical scrubbing, or pulsed air.
And are analogous to autoclaving, and when performed correctly renders food sterile.Moist heat causes destruction of micro-organisms by denaturation of macromolecules, primarily proteins. This method is a faster process than dry heat sterilization. Dry heat sterilizerDry heat was the first method of sterilization, and is a longer process than moist heat sterilization. The destruction of microorganisms through the use of dry heat is a gradual phenomenon. With longer exposure to lethal temperatures, the number of killed microorganisms increases. 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. At higher temperatures, shorter exposure times are required to kill organisms.
This can reduce heat-induced damage to food products.The standard setting for a hot air oven is at least two hours at 160 °C. A rapid method heats air to 190 °C for 6 minutes for unwrapped objects and 12 minutes for wrapped objects.
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). FlamingFlaming is done to loops and straight-wires in microbiology labs. Leaving the loop in the flame of a 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 inoculating loop with a heated cage, ensuring that such sprayed material does not further contaminate the area. Another problem is that gas flames may leave carbon or other residues on the object if the object is not heated enough.
A variation on flaming is to dip the object in 70% or higher, then briefly touch the object to a flame. The ethanol will ignite and burn off rapidly, leaving less residue than a gas flame. IncinerationIncineration is a waste treatment process that involves the combustion of organic substances contained in waste materials. This method also burns any organism to ash. Pioneer cd player pd m502.
It is used to sterilize medical and other biohazardous waste before it is discarded with non-hazardous waste. Bacteria incinerators are mini furnaces used to incinerate and kill off any micro organisms that may be on an inoculating loop or wire. TyndallizationNamed after, Tyndallization is an obsolete and 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, 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. 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, and will not sterilize non-nutritive substrates like water. Tyndallization is also ineffective against prions. Glass bead sterilizersGlass bead sterilizers work by heating glass beads to 250 °C.
Instruments are then quickly doused in these glass beads, which heat the object while physically scraping contaminants off their surface. Glass bead sterilizers were once a common sterilization method employed in offices as well as biologic laboratories, but are not approved by the (FDA) and (CDC) to be used as a sterilizers since 1997. They are still popular in as well as dental practices although there are no current guidelines for using this sterilizer. Chemical sterilization. ChemiclavChemicals are also used for sterilization. Heating provides a reliable way to rid objects of all transmissible agents, but it is not always appropriate if it will damage heat-sensitive materials such as biological materials, electronics, and many. In these situations chemicals, either as gases or in liquid form, can be used as sterilants.
While the use of gas and liquid chemical sterilants avoids the problem of heat damage, users must ensure that article to be sterilized is chemically compatible with the sterilant being used. In addition, the use of chemical sterilants poses new challenges for workplace safety, as the properties that make chemicals effective sterilants usually make them harmful to humans. 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 sterilization method, used for approximately 70% of total sterilizations, and for over 50% of all disposable medical devices.Ethylene oxide treatment is generally carried out between 30 °C and 60 °C with relative humidity above 30% and a gas concentration between 200 and 800 mg/l. Typically, the process lasts for several hours. Ethylene oxide is highly effective, as it penetrates all porous materials, and it can penetrate through some plastic materials and films.
Ethylene oxide kills all known microorganisms such as bacteria (including spores), viruses, and fungi (including yeasts and molds), and is compatible with almost all materials even when repeatedly applied. It is flammable, toxic and carcinogenic, however, with a reported potential for some adverse health effects when not used in compliance with published requirements. Ethylene oxide sterilizers and processes require biological after sterilizer installation, significant repairs or process changes.The traditional process consists of a preconditioning phase (in a separate room or cell), a processing phase (more commonly in a vacuum vessel and sometimes in a pressure rated vessel), and an aeration phase (in a separate room or cell) to remove ethylene oxide residues and lower by-products such as ethylene chlorohydrin (EC or ECH) and, of lesser importance, (EG). An alternative process, known as all-in-one processing, also exists for some products whereby all three phases are performed in the vacuum or pressure rated vessel. This latter option can facilitate faster overall processing time and residue dissipation.The most common ethylene oxide processing method is the gas chamber method. To benefit from, ethylene oxide has traditionally been delivered by filling a large chamber with a combination of gaseous ethylene oxide either as pure ethylene oxide, or with other gases used as diluents (chlorofluorocarbons , hydrochlorofluorocarbons (HCFCs), or ).Ethylene oxide is still widely used by medical device manufacturers. Since ethylene oxide is explosive at concentrations above 3%, ethylene oxide was traditionally supplied with an inert carrier gas such as a CFC or HCFC.
The use of CFCs or HCFCs as the carrier gas was banned because of concerns of ozone depletion. These halogenated hydrocarbons are being replaced by systems using 100% ethylene oxide because of regulations and the high cost of the blends. In hospitals, most ethylene oxide sterilizers use single use cartridges because of the convenience and ease of use compared to the former plumbed gas cylinders of ethylene oxide blends.It is important to adhere to patient and healthcare personnel government specified limits of ethylene oxide residues in and/or on processed products, operator exposure after processing, during storage and handling of ethylene oxide gas cylinders, and environmental emissions produced when using ethylene oxide.The U.S.
Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit (PEL) at 1 ppm calculated as an eight-hour time weighted average (TWA) 29 CFR 1910.1047 and 5 ppm as a 15-minute excursion limit (EL). The National Institute for Occupational Safety and Health (NIOSH) immediately dangerous to life and health limit (IDLH) for ethylene oxide is 800 ppm. The odor threshold is around 500 ppm, so ethylene oxide is imperceptible until concentrations well above the OSHA PEL. Therefore, OSHA recommends that continuous gas monitoring systems be used to protect workers using ethylene oxide for processing.
Employees' health records must be maintained during employment and after termination of employment for 30 years. Nitrogen dioxide(NO 2) 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 NO 2 gas allow for sterilant dispersion in an enclosed environment at room temperature and ambient pressure. The mechanism for lethality is the degradation of DNA in the spore core through nitration of the phosphate backbone, which kills the exposed organism as it absorbs NO 2.
This degradation occurs at even very low concentrations of the gas. NO 2 has a boiling point of 21 °C at sea level, which results in a relatively high saturated vapor pressure at ambient temperature. Because of this, liquid NO 2 may be used as a convenient source for the sterilant gas. Liquid NO 2 is often referred to by the name of its dimer, (N 2O 4).
Additionally, the low levels of concentration required, coupled with the high vapor pressure, assures that no condensation occurs on the devices being sterilized. This means that no aeration of the devices is required immediately following the sterilization cycle. NO 2 is also less corrosive than other sterilant gases, and is compatible with most medical materials and adhesives.The most-resistant organism (MRO) to sterilization with NO 2 gas is the spore of, which is the same MRO for both steam and hydrogen peroxide sterilization processes.
The spore form of G. Stearothermophilus has been well characterized over the years as a in sterilization applications. Microbial inactivation of G. Stearothermophilus with NO 2 gas proceeds rapidly in a log-linear fashion, as is typical of other sterilization processes.
Noxilizer, Inc. Has commercialized this technology to offer contract sterilization services for at its Baltimore, MD facility. This has been demonstrated in Noxilizer’s lab in multiple studies and is supported by published reports from other labs. These same properties also allow for quicker removal of the sterilant and residuals through aeration of the enclosed environment. The combination of rapid lethality and easy removal of the gas allows for shorter overall cycle times during the sterilization (or decontamination) process and a lower level of sterilant residuals than are found with other sterilization methods. Ozoneis 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.Ozone offers many advantages as a sterilant gas; ozone is a very efficient sterilant because of its strong oxidizing properties (E = 2.076 vs SHE ) capable of destroying a wide range of pathogens, including prions without the need for handling hazardous chemicals since the ozone is generated within the sterilizer from medical grade oxygen. The high reactivity of ozone means that waste ozone can be destroyed by passing over a simple catalyst that reverts it to oxygen and ensures that the cycle time is relatively short. The disadvantage of using ozone is that the gas is very reactive and very hazardous.
The NIOSH immediately dangerous to life and health limit for ozone is 5 ppm, 160 times smaller than the 800 ppm IDLH for ethylene oxide. Documentation for Immediately Dangerous to Life or Health Concentrations (IDLH): NIOSH Chemical Listing and Documentation of Revised IDLH Values (as of 3/1/95) and OSHA has set the PEL for ozone at 0.1 ppm calculated as an 8 hour time weighted average (29 CFR 1910.1000, Table Z-1). The Canadian Center for Occupation Health and Safety provides an excellent summary of the health effects of exposure to ozone. The sterilant gas manufacturers include many safety features in their products but prudent practice is to provide continuous monitoring to below the OSHA PEL to provide a rapid warning in the event of a leak.
Monitors for determining workplace exposure to ozone are commercially available. Glutaraldehyde and formaldehydeand solutions (also used as ) 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 22 hours with glutaraldehyde and even longer with formaldehyde. The presence of solid particles may lengthen 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 ( 10% w/w). The vapor is also hazardous, primarily affecting the eyes and respiratory system.
Even short term exposures can be hazardous and NIOSH has set the Immediately Dangerous to Life and Health Level (IDLH) at 75 ppm, less than one tenth the IDLH for ethylene oxide (800 ppm). Prolonged exposure to lower concentrations can cause permanent lung damage and consequently OSHA has set the permissible exposure limit to 1.0 ppm, calculated as an 8-hour time weighted average. Sterilizer manufacturers go to great lengths to make their products safe through careful design and incorporation of many safety features, though there are still workplace exposures of hydrogen peroxide from gas sterilizers are documented in the FDA MAUDE database. When using any type of gas sterilizer, prudent work practices will include good ventilation, a continuous gas monitor for hydrogen peroxide and good work practices and training.(VHP) is used to sterilize large enclosed and sealed areas such as entire rooms and aircraft interiors. Peracetic acid(0.2%) is a recognized sterilant by the FDA for use in sterilizing medical devices such as. Potential for chemical sterilization of prionsPrions are highly resistant to chemical sterilization.
Treatment with such as 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., formaldehyde, glutaraldehyde and peracetic acid also fail this test (one hour treatment). Only, and sodium hydroxide (NaOH) reduce prion levels by more than 4 logs; chlorine (too corrosive to use on certain objects) and NaOH are the most consistent. Many studies have shown the effectiveness of sodium hydroxide. Radiation sterilizationSterilization can be achieved using such as, or irradiation.
Electromagnetic or particulate radiation can be energetic enough to ionize atoms or molecules , or less energetic. Non-ionizing radiation sterilizationirradiation (UV, from a ) is useful for sterilization of surfaces and some transparent objects. Many objects that are transparent to absorb UV. UV irradiation is routinely used to sterilize the interiors of 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 some plastics, such as foam if exposed for prolonged periods of time. Efficiency illustration of the different radiation technologies (electron beam, X-ray, gamma rays)The safety of irradiation facilities is regulated by the and monitored by the different national Nuclear Regulatory Commissions. The incidents that have occurred in the past are documented by the agency and thoroughly analyzed to determine root cause and improvement potential.
Such improvements are then mandated to retrofit existing facilities and future design.Gamma radiation is very penetrating, and is commonly used for sterilization of disposable medical equipment, such as syringes, needles, and IV sets, and food. It is emitted by a, usually ( 60Co) or ( 137Cs).Use of a radioisotope requires shielding for the safety of the operators while in use and in storage.
With most designs the radioisotope is lowered into a water-filled source storage pool, which absorbs radiation and allows maintenance personnel to enter the radiation shield. One variant keeps the radioisotope under water at all times and lowers the product to be irradiated into the water towards the source in hermetic bells; no further shielding is required for such designs. Other uncommonly used designs use dry storage, providing movable shields that reduce radiation levels in areas of the irradiation chamber.
An incident in, US, where water-soluble caesium-137 leaked into the source storage pool, requiring intervention has led to use of this radioisotope being almost entirely discontinued in favour of the more costly, non-water-soluble cobalt-60. Cobalt-60 gamma have about twice the energy, and hence greater penetrating range, of Caesium-137 radiation.is also commonly used for sterilization.
Electron beams use an on-off technology and provide a much higher dosing rate than gamma or x-rays. Due to the higher dose rate, less exposure time is needed and thereby any potential degradation to polymers is reduced. A limitation is that electron beams are less penetrating than either gamma or x-rays. Facilities rely on substantial concrete shields to protect workers and the environment from radiation exposure.X-rays: high-energy X-rays (produced by bremsstrahlung) allow irradiation of large packages and loads of medical devices.
They are sufficiently penetrating to treat multiple pallet loads of low-density packages with very good dose uniformity ratios. X-ray sterilization does not require chemical or radioactive material: high-energy X-rays are generated at high intensity by an that does not require shielding when not in use. X-rays are generated by bombarding a dense material (target) such as or with high-energy electrons in a process known as conversion. These systems are energy-inefficient, requiring much more electrical energy than other systems for the same result.with X-rays or gamma rays, electromagnetic radiation rather than, does not make materials. 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.Sterilization by irradiation with gamma rays may however in some cases affect material properties.Irradiation is used by the to sterilize mail in the area. Some foods (e.g. Spices, ground meats) are.Subatomic particles may be more or less penetrating, and may be generated by a radioisotope or a device, depending upon the type of particle.
Sterile filtrationFluids that would be damaged by heat, irradiation or chemical sterilization, such as drug products, can be sterilized by using. This method is commonly used for heat labile pharmaceuticals and solutions in medicinal drug processing. A microfilter with pore size 0.2 will usually effectively remove. In the processing of b, must be removed or inactivated, requiring the use of with a smaller pore size (20 -50 ) are used. Smaller pore sizes lower the flow rate, so in order to achieve higher total throughput or to avoid premature blockage, pre-filters might be used to protect small pore membrane filters.Membrane filters used in production processes are commonly made from materials such as mixed cellulose ester or (PES). The filtration equipment and the filters themselves may be purchased as pre-sterilized 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 proper functioning of the filter, the membrane filters are integrity tested post-use and sometimes before use. The non-destructive integrity test assures the filter is undamaged, and is a regulatory requirement. Typically, terminal pharmaceutical sterile filtration is performed inside of a to prevent contamination. Preservation of sterility.
Medicine and surgeryIn 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. Examples of such instruments include,. This is also essential in the manufacture of pharmaceuticals.Heat sterilization of medical instruments is known to have been used in, but it mostly disappeared throughout the resulting in significant increases in disability and death following surgical procedures.Preparation of injectable medications and intravenous solutions for therapy requires not only a high, but well-designed containers to prevent entry of after initial sterilization.Compare sterilisation to which reduces the number of viable organisms to an acceptable level.
An example of the latter is. Heat sterilization. Front-loading autoclavesA widely-used method for heat sterilization is the, sometimes called a converter. Autoclaves commonly use steam heated to 121–134 °C (250–273 °F).
To achieve sterility, a holding time of at least 15 minutes at 121 °C (250 °F) or 3 minutes at 134 °C (273 °F) is required. Additional sterilizing time is usually required for liquids and instruments packed in layers of cloth, as they may take longer to reach the required temperature (unnecessary in machines that grind the contents prior to sterilization). Following sterilization, liquids in a pressurized autoclave must be cooled slowly to avoid boiling over when the pressure is released.
Modern converters operate around this problem by gradually depressing the sterilization chamber and allowing liquids to evaporate under a negative pressure, while cooling the contents.Proper autoclave treatment will inactivate all, bacteria, viruses and also bacterial, which can be quite resistant. It will not necessarily eliminate all.For prion elimination, various recommendations state 121–132 °C (250–270 °F) for 60 minutes or 134 °C (273 °F) for at least 18 minutes.
The prion that causes the disease (strain 263K) is inactivated relatively quickly by such sterilization procedures; however, other strains of scrapie, as well as strains of and are more resistant. Using as test animals, one experiment showed that heating BSE positive tissue at 134–138 °C (273–280 °F) for 18 minutes resulted in only a 2.5 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 (formerly ), among the toughest organisms for an autoclave to destroy.
Typically these devices have a self-contained liquid growth medium and a growth indicator. After autoclaving an internal glass ampule is shattered, releasing the spores into the growth medium. The vial is then incubated (typically at 56 °C (133 °F)) for 24 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. Alternatively steam penetration can be achieved by shredding the waste in some Autoclave models that also render the end product unrecognizable. During the initial heating of the chamber, residual air must be removed.
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 or 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 or pulsed air can also be used to remove debris. See also: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 utensilsoften 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), it clearly 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. Other methodsOther heat methods include flaming, and using dry heat.Flaming is done to loops and straight-wires in microbiology labs.
Leaving the loop in the flame of a 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 inoculating loop with a heated cage, ensuring that such sprayed material does not further contaminate the area.
Another problem is that gas flames may leave residues on the object, e.g. Carbon, if the object is not heated enough.A variation on flaming is to dip the object in 70% (or a higher concentration) and merely touch the object briefly to the Bunsen burner flame, but not hold it in the gas flame. The ethanol will ignite and burn off in a few seconds. 70% ethanol kills many, but not all, bacteria and viruses, and has the advantage that it leaves less residue than a gas flame. This method works well for the glass 'hockey stick'-shaped bacteria spreaders.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 fifteen minutes will kill most vegetative bacteria and inactivate viruses, but boiling is ineffective against and many bacterial and fungal; 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 people, requiring only water, enough heat, and a container that can withstand the heat; however, boiling can be hazardous and cumbersome./ Tyndallization named after 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 sterilisatorDry 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. 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).can be inactivated by immersion in (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 treatment. However, sodium hydroxide may corrode surgical instruments, especially at the elevated temperatures of the autoclave.Glass bead sterilizer, once a common sterilization method employed in offices as well as biologic laboratories, is not approved by the (FDA) and (CDC) to be used as inter- sterilizer since 1997. Still it is popular in as well as dental practice although there are no current guidelines for using this sterilizer. Chemical sterilization.
ChemiclavChemicals 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, electronics, and many.
Low temperature gas sterilizers function by exposing the articles to be sterilized to high concentrations (typically 5 - 10% v/v) of very reactive gases (alkylating agents such as ethylene oxide, and oxidizing agents such as hydrogen peroxide and ozone). Liquid sterilants and high disinfectants typically include oxidizing agents such as hydrogen peroxide and peracetic acid and aldehydes such as glutaraldehyde and more recently o-phthalaldehyde. While the use of gas and liquid chemical sterilants/high level disinfectants avoids the problem of heat damage, users must ensure that article to be sterilized is chemically compatible with the sterilant being used.
The manufacturer of the article can provide specific information regarding compatible sterilants. In addition, the use of chemical sterilants poses new challenges for workplace safety. The chemicals used as sterilants are designed to destroy a wide range of pathogens and typically the same properties that make them good sterilants makes them harmful to humans. Employers have a duty to ensure a safe work environment (Occupational Safety and Health Act of 1970, section 5 for United States) and work practices, engineering controls and monitoring should be employed appropriately. 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 and 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 costsEthylene oxide is still widely used by medical device manufacturers for larger scale sterilization (e.g.
By the pallet), but while still used, EtO is becoming less popular in hospitals. Since Eto is explosive from its lower explosive limit of 3% all the way to 100%, EtO was traditionally supplied with an inert carrier gas such as a CFC or halogenated hydrocarbon. The use of CFCs as the carrier gas was banned because of concerns of ozone depletion and halogenated hydrocarbons are being replaced by so-called 100% EtO systems because of the much greater cost of the blends.
In hospitals, most EtO sterilizers use single use cartridges (e.g. 3M's Steri-Vac line, or Steris Corporation's Stericert sterilizers) because of the convenience and ease of use compared to the former plumbed gas cylinders of EtO blends. Another 100% method is the so-called micro-dose sterilization method, developed in the late 1950s, using a specially designed bag to eliminate the need to flood a larger chamber with EtO. This method is also known as, or bag sterilization. This method minimizes the use of gas.Another reason for the decrease in use of EtO are the well known health effects.
In addition to being a primary irritant, EtO is now classified by the IARC as a known human carcinogen. The US OSHA has set the permissible exposure limit (PEL) at 1 ppm calculated as an eight hour time weighted average (TWA) 29 CFR 1910.1047 and 5 ppm as a 15 minute TWA. The NIOSH Immediately dangerous to life and health limit for EtO is 800 ppm. The odor threshold is around 500 ppm and so EtO is imperceptible until concentrations well above the OSHA PEL. Therefore, OSHA recommends that some kind of continuous gas monitoring system be used to protect workers using EtO for sterilization.
While the hazards of EtO are generally well known, it should be noted that all chemical sterilants are designed to kill a broad spectrum of organisms, by exposing them to high concentrations of reactive chemicals. Therefore, it is no surprise that all the common chemical gas sterilants are toxic and adequate protective measures must be taken to protect workers using these materials. Spore testing, a very resistant organism, is used as a rapid biological indicator for EO sterilizers. If sterilization fails, incubation at 37 °C causes a 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. Ozoneis 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.Ozone offers many advantages as a sterilant gas; ozone is a very efficient sterilant because of its strong oxidizing properties (E = 2.076 vs SHE, CRC Handbook of Chemistry and Physics, 76th Ed, 1995-1996) capable of destroying a wide range of pathogens, including prions without the need for handling hazardous chemicals since the ozone is generated within the sterilizer from medical grade oxygen. In 2005 a Canadian company called TSO3 Inc received FDA clearance to sell an ozone sterilizer for use in healthcare. The high reactivity of ozone means that waste ozone can be destroyed by passing over a simple catalyst that reverts it back to oxygen and also means that the cycle time is relatively short (about 4.5 hours for TSO3's model 125L).
The downside of using ozone is that the gas is very reactive and very hazardous. The NIOSH immediately dangerous to life and health limit for ozone is 5 ppm, much 160 times smaller than the 800 ppm IDLH for ethylene oxide.
And OSHA has set the PEL for ozone at 0.1 ppm calculated as an eight hour time weighted average (29 CFR 1910.1000, Table Z-1). The Canadian Center for Occupation Health and Safety provides an excellent summary of the health effects of exposure to ozone. The sterilant gas manufacturers include many safety features in their products but prudent practice is to provide continuous monitoring to below the OSHA PEL to provide a rapid warning in the even of a leak and monitors for determining workplace exposure to ozone are commercially available.
Bleachis another accepted liquid sterilizing agent. Household bleach consists of 5.25%.
It is usually diluted to 1/10 immediately before use; however to kill it should be diluted only 1/5, and 1/2.5 (1 part bleach and 1.5 parts water) to inactivate. The dilution factor must take into account the volume of any liquid waste that it is being used to sterilize. 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.Bleach decomposes over time when exposed to air, so fresh solutions should be made daily. Glutaraldehyde and Formaldehydeand solutions (also used as ) 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 lengthen 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 (.
Hydrogen Peroxideis another chemical sterilizing agent. It is relatively non-toxic when diluted to low concentrations, such as the familiar 3% retail solutions although hydrogen peroxide is a dangerous oxidizer at high concentrations ( 10% w/w). Hydrogen peroxide is strong oxidant and these oxidizing properties allow it to destroy a wide range of pathogens and it is used to sterilize heat or temperature sensitive articles such as rigid endoscopes.
In medical sterilization hydrogen peroxide is used at higher concentrations, ranging from around 35% up to 90%. The biggest advantage of hydrogen peroxide as a sterilant is the short cycle time.
Whereas the cycle time for ethylene oxide (discussed above) may be 10 to 15 hours, the use of very high concentrations of hydrogen peroxide allows much shorter cycle times. Some hydrogen peroxide modern sterilizers, such as the Sterrad NX have a cycle time as short as 28 minutes.Hydrogen peroxide sterilizers have their drawbacks. Since hydrogen peroxide is a strong oxidant, there are material compatibility issues and users should consult the manufacturer of the article to be sterilized to ensure that it is compatible with this method of sterilization. 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. The penetrating ability of hydrogen peroxide is not as good as ethylene oxide and so there are limitations on the length and diameter of lumens that can be effectively sterilized and guidance is available from the sterilizer manufacturers.While hydrogen peroxide offers significant advantages in terms of throughput, as with all sterilant gases, sterility is achieved through the use of high concentrations of reactive gases.
Hydrogen peroxide is primary irritant and the contact of the liquid solution with skin will cause bleaching or ulceration depending on the concentration and contact time. The vapor is also hazardous with the target organs being the eyes and respiratory system.
Even short term exposures can be hazardous and NIOSH has set the Immediately Dangerous to Life and Health Level (IDLH) at 75 ppm. Less than one tenth the IDLH for ethylene oxide (800 ppm).
Prolonged exposure to even low ppm concentrations can cause permanent lung damage and consequently OSHA has set the permissible exposure limit to 1.0 ppm, calculated as an 8 hour time weighted average (29 CFR 1910.1000 Table Z-1). Employers thus have a legal duty to ensure that their personnel are not exposed to concentrations exceeding this PEL. Even though the sterilizer manufacturers go to great lengths to make their products safe through careful design and incorporation of many safety features, workplace exposures of hydrogen peroxide from gas sterilizers are documented in the FDA MAUDE database.
When using any type of gas sterilizer, prudent work practices will include good ventilation (10 air exchanges per hour), a continuous gas monitor for hydrogen peroxide as well as good work practices and training. Further information about the health effects of hydrogen peroxide and good work practices is available from OSHA and the ATSDR.Hydrogen peroxide can also be mixed with 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 (18 to 27 °F).
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. Prionsare highly resistant to chemical sterilization. Treatment with (e.g., ) 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., glutaraldehyde and peracetic acid also fail this test (one hour treatment). Only, a, and (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. SilverSilver ions and silver compounds show a toxic effect on some bacteria, viruses, algae and fungi, typical for heavy metals like or, but without the high toxicity to humans that is normally associated with these other metals. Its germicidal effects kill many microbial organisms, but testing and standardization of silver products is yet difficult., the father of modern medicine, wrote that silver had beneficial healing and anti-disease properties, and the used to store water, and in silver bottles to prevent spoiling. In the early 1900s people would put in milk bottles to prolong the milk's freshness. The exact process of silver's germicidal effect is still not well understood. One of the explanations is the, which accounts for the effect on microorganisms but not on viruses.Silver compounds were used to prevent infection in before the advent of.
Silver nitrate solution was a standard of care but was largely replaced by cream (SSD Cream), which was generally the 'standard of care' for the antibacterial and antibiotic treatment of serious burns until the late 1990s. Now, other options, such as silver-coated dressings (activated silver dressings), are used in addition to SSD cream. However, the evidence for the use of such silver-treated dressings is mixed and although the evidence on if they are effective is promising, it is marred by the poor quality of the trials used to assess these products. Consequently a major by the found insufficient evidence to recommend the use of silver-treated dressings to treat infected wounds.The widespread use of silver went out of fashion with the development of antibiotics.
Types Of Sterilization Methods
However, recently there has been renewed interest in silver as a broad-spectrum antimicrobial. In particular, silver is being used with, a naturally occurring derived from seaweed, in a range of products designed to prevent infections as part of management procedures, particularly applicable to victims. In 2007, introduced the first antibacterial glass to fight hospital-caught infection: it is covered with a thin layer of silver. In addition, has introduced with a final rinse containing silver ions to provide several days of antibacterial protection in the clothes. Has introduced a line of that have silver ions embedded to kill germs. A company called Thomson Research Associates has begun treating products with Ultra Fresh, an anti-microbial technology involving 'proprietary nano-technology to produce the ultra-fine silver particles essential to ease of application and long-term protection.'
The (FDA) has recently approved an with a fine coat of silver for use in, after studies found it reduced the risk of ventilator-associated.It has long been known that antibacterial action of silver is enhanced by the presence of an. Applying a few volts of electricity across silver electrodes drastically enhances the rate that bacteria in solution are killed. It was found recently that the antibacterial action of silver electrodes is greatly improved if the electrodes are covered with silver nanorods. Note that enhanced antibacterial properties of nanoparticles compared to bulk material is not limited to silver, but has also been demonstrated on other materials such as Radiation SterilizationMethods of sterilization exist using such as, or. are very penetrating and are commonly used for sterilization of disposable medical equipment, such as syringes, needles, and IV sets.
Gamma radiation requires bulky shielding for the safety of the operators; they also require storage of a (usually ), which continuously emits gamma rays (it cannot be turned off, and therefore always presents a hazard in the area of the facility). is also commonly used for medical device sterilization. Electron beams use an on-off technology and provide a much higher dosing rate than gamma or x-rays. Due to the higher dose rate, less exposure time is needed and thereby any potential degradation to polymers is reduced. A limitation is that electron beams are less penetrating than either gamma or x-rays., High-energy X-rays (bremsstrahlung) are a form of ionizing energy allowing to irradiate large packages and pallet loads of medical devices.
Their penetration is sufficient to treat multiple pallet loads of low-density packages with very good dose uniformity ratios. X-ray sterilization is an electricity based process not requiring chemical nor radio-active material. High energy and high power X-rays are generated by an that can be turned off for servicing and when not in use. irradiation (UV, from a ) is useful only for sterilization of surfaces and some transparent objects. Many objects that are transparent to absorb UV. UV irradiation is routinely used to sterilize the interiors of 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 foam. Further information:.
Subatomic particles may be more or less penetrating, and may be generated by a radioisotope or a device, depending upon the type of particle.with or does not make materials. 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 to sterilize mail in the area. Some foods (e.g. Spices, ground meats) are irradiated for sterilization (see ). Sterile filtrationClear 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 solutions in biological research. A filter with pore size 0.2 will effectively remove. If must also be removed, a much smaller pore size around 20 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 pre-sterilized 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.To ensure the best results, pharmaceutical sterile filtration is performed in a room with highly filtered air ( filtration) or in a or 'flowbox', a device which produces a stream of HEPA filtered air.
Sterilization Methods In Microbiology Pdf Free
See also.References. Mesquita, J. M.; Teixeira, M.A. And Brandao, S. Retrieved 2007-03-06.
Thiel, Theresa (1999). Science in the Real World. Retrieved 2007-03-06.
^ Zadik Y, Peretz A (Apr 2008). 'The effectiveness of glass bead sterilizer in the dental practice'. J Isr Dent Assoc 25 (2): 36–9. 2008-09-11. ^. Biosafety Manual (2004 edition). Office of Health and Safety (2007).
(5th ed.). Chopra I (April 2007). 'The increasing use of silver-based products as antimicrobial agents: a useful development or a cause for concern?' The Journal of antimicrobial chemotherapy 59 (4): 587–90. Chang TW, Weinstein L (December 1975).
Agents Chemother. 8 (6): 677–8.&. Atiyeh BS, Costagliola M, Hayek SN, Dibo SA (March 2007). 'Effect of silver on burn wound infection control and healing: review of the literature'. Burns: journal of the International Society for Burn Injuries 33 (2): 139–48. ^ Lo SF, Hayter M, Chang CJ, Hu WY, Lee LL (August 2008).
'A systematic review of silver-releasing dressings in the management of infected chronic wounds'. Journal of clinical nursing 17 (15): 1973–85. Hermans MH (December 2006). 'Silver-containing dressings and the need for evidence'. The American journal of nursing 106 (12): 60–8; quiz 68–9. Retrieved 2007-08-06.
Express Textile. Retrieved 2007-11-11. O. Akhavan and E. Ghaderi 'Enhancement of antibacterial properties of Ag nanorods by electric field' Sci. 10 (2009) 015003. N.
Padmavathy et al. 'Enhanced bioactivity of ZnO nanoparticles—an antimicrobial study' Sci.
9 (2007) 035004., IAEA, Vienna,24 September 2008.