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发帖数: 25265 | 1 Sterilization (microbiology)
http://en.wikipedia.org/wiki/Sterilization_(microbiology)
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Contents [hide]
1 Applications
1.1 Foods
1.2 Medicine and surgery
2 Heat sterilization
2.1 Steam sterilization utensils
2.2 Food
2.3 Other methods
3 Chemical sterilization
3.1 Ethylene Oxide
3.2 Ozone
3.3 Bleach
3.4 Glutaraldehyde and Formaldehyde
3.5 Phthalaldehyde
3.6 Hydrogen Peroxide
3.7 Dry sterilization process
3.8 Peracetic acid
3.9 Prions
3.10 Silver
4 Radiation sterilization
5 Sterile filtration
6 Cleaning methods that do not achieve sterilization
7 See also
8 References
8.1 Notes
8.2 General references
Sterilization (or sterilisation, see spelling differences) is a term
referring to any process that eliminates (removes) or kills all forms of
life, including transmissible agents (such as fungi, bacteria, viruses,
spore forms, etc.) present on a surface, contained in a fluid, in medication
, or in a compound such as biological culture media.[1][2] Sterilization can
be achieved by applying the proper combinations of heat, chemicals,
irradiation, high pressure, and filtration.
The term has evolved to include the disabling or destruction of infectious
proteins such as prions related to Transmissible Spongiform Encephalopathies
(TSE).[3]
[edit] Applications[edit] FoodsOne of the first steps toward sterilization
was made by Nicolas Appert.
He learned that thorough cooking (applying a suitable amount of heat over a
suitable period of time) slowed the decay of foods and various liquids,
preserving them for safe consumption for a longer time than was typical.
Canning of foods is an extension of the same principle, and has helped to
reduce food borne illness ("food poisoning"). Other methods of sterilizing
foods include food irradiation[4] and pascalization (the use of high
pressure to kill microorganisms).[5]
[edit] Medicine and surgeryIn general, surgical instruments and medications
that enter an already aseptic part of the body (such as the bloodstream, or
penetrating the skin) must be sterilized to a high sterility assurance level
, or SAL. Examples of such instruments include scalpels, hypodermic needles
and artificial pacemakers. This is also essential in the manufacture of
parenteral pharmaceuticals.
Heat (flame) 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
also well-designed containers to prevent entry of adventitious agents after
initial product sterilization.
Sterilization as a definition terminates all life; whereas sanitization and
disinfection terminates selectively and partially. Both sanitization and
disinfection reduce the number of targeted [pathogenic] organisms to what
are considered "acceptable" levels - levels that a reasonably healthy,
intact, body can deal with. An example of this class of process is
Pasteurization.
[edit] Heat sterilizationSee also: Dry heat sterilization and Moist heat
sterilization
[edit] Steam sterilization utensils
Front-loading autoclavesA widely-used method for heat sterilization is the
autoclave, 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 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 (250–270
°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 Geobacillus stearothermophilus (formerly 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. 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 retain 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 ultrasound or pulsed air can
also be used to remove debris.
[edit] FoodSee also: Food safety
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.
[edit] Other methodsOther 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 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% ethanol (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.
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 fifteen minutes will kill most vegetative bacteria and
inactivate 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
people, requiring only water, enough heat, and a container that can
withstand the heat; however, boiling can be hazardous and cumbersome.
Tindalization[6] /Tyndallization[7] 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 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.[8][9
] 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 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 dental
offices as well as biologic laboratories,[10] is not approved by the U.S.
Food and Drug Administration (FDA) and Centers for Disease Control and
Prevention (CDC) to be used as inter-patients sterilizer since 1997.[11]
Still it is popular in European as well as Israeli dental practice although
there are no current evidence-based guidelines for using this sterilizer.[10]
[edit] 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, fiber optics, electronics, and many
plastics. 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.
[edit] Ethylene OxideEthylene oxide (EO or EtO) gas is commonly used to
sterilize objects sensitive to temperatures greater than 60 °C and / or
radiation 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, and typically
lasts for at least three hours. Ethylene oxide penetrates well, moving
through paper, cloth, and some plastic films and is highly effective. EtO
can kill all known viruses, bacteria and fungi, including bacterial spores
and is compatible with most materials (e.g. of medical devices), even when
repeatedly applied. However, it is highly flammable, toxic and carcinogenic.
A typical process consists of a preconditioning phase, the actual
sterilization run and a period of post-sterilization aeration to remove
toxic residues, such as ethylene oxide residues and by-products such
ethylene glycol (formed out of EtO and ambient humidity) and ethylene
chlorohydrine (formed out of EtO and materials containing chlorine, such as
PVC). Besides moist heat and irradiation, 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.
Ethylene 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
[12] 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,[13] or
Steris Corporation's Stericert sterilizers[14]) 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 gas
diffusion sterilization, or bag sterilization. This method minimizes the use
of gas.[15]
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.[16] 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.[17]
The odor threshold is around 500 ppm[18] 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.[19] 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.
[edit] OzoneOzone 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.
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[20] 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[21] 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.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 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.[22] 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 and monitors for
determining workplace exposure to ozone are commercially available.
[edit] BleachChlorine 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, and 1/2.5 (1 part bleach and 1.5
parts water) to inactivate prions. The dilution factor must take into
account the volume of any liquid waste that it is being used to sterilize.[
23] 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 also highly corrosive.
Bleach decomposes over time when exposed to air, so fresh solutions should
be made daily.[24]
[edit] Glutaraldehyde and FormaldehydeGlutaraldehyde 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 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 (<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.
[edit] PhthalaldehydeOrtho-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. Some side effects from equipment sterilized using this
reagent have been reported. For example, two cases of anaphylaxis following
cystoscopy with endoscopes sterilized with OPA were reported by Cooper, et
al., (J Endourol. 2008 Sep;22(9):2181-4), and four cases of ortho-
phthalaldehyde-induced anaphylaxis after laryngoscopy with the detection of
specific IgE in serum were reported by Suzukawa, et al., (Allergol Int. 2007
Sep;56(3):313-6. Epub 2007 Jul 1; J Allergy Clin Immunol. 2006 Jun;117(6):
1500-1. Epub 2006 Mar 31).
[edit] Hydrogen PeroxideHydrogen peroxide is 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.[17] 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.[25]
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[26] and the ATSDR.[27]
Hydrogen peroxide can also be mixed with formic acid 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.
[edit] Dry sterilization processDry 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.
[edit] Peracetic acidPeracetic acid (0.2%) is used to sterilize instruments
in the Steris system.
[edit] PrionsPrions 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.
[edit] SilverSilver ions and silver compounds show a toxic effect on some
bacteria, viruses, algae and fungi, typical of heavy metals like lead or
mercury, but without the high toxicity to humans that is normally associated
with these other metals. Its germicidal effects kill many microbial
organisms in vitro, but testing and standardization of silver products is
yet difficult.[28]
Hippocrates, the father of modern medicine, wrote that silver had beneficial
healing and anti-disease properties[cite this quote], and the Phoenicians
used to store water, wine, and vinegar in silver bottles to prevent spoiling
. In the early 1900s people would put silver dollars in milk bottles to
prolong the milk's freshness.[29] The exact process of silver's germicidal
effect is still not well understood. One of the explanations is the
oligodynamic effect, which accounts for the effect on microorganisms but not
on viruses.
Silver compounds were used to prevent infection in World War I before the
advent of antibiotics. Silver nitrate solution was a standard of care but
was largely replaced by silver sulfadiazine cream (SSD Cream),[30] which was
generally the "standard of care" for the antibacterial and antibiotic
treatment of serious burns until the late 1990s.[31] 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.[32] Consequently a major systematic review by the
Cochrane Collaboration found insufficient evidence to recommend the use of
silver-treated dressings to treat infected wounds.[32]
The widespread use of silver went out of fashion with the development of
antibiotics. However, recently there has been renewed interest in silver as
a broad-spectrum antimicrobial. In particular, silver is being used with
alginate, a naturally occurring biopolymer derived from seaweed, in a range
of products designed to prevent infections as part of wound management
procedures, particularly applicable to burn victims.[33] In 2007, AGC Flat
Glass Europe introduced the first antibacterial glass to fight hospital-
caught infection: it is covered with a thin layer of silver.[34] In addition
, Samsung has introduced washing machines with a final rinse containing
silver ions to provide several days of antibacterial protection in the
clothes.[35] Kohler has introduced a line of toilet seats 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."[36]
The U.S. Food and Drug Administration (FDA) has recently approved an
endotracheal breathing tube with a fine coat of silver for use in mechanical
ventilation, after studies found it reduced the risk of ventilator-
associated pneumonia.[37]
It has long been known that antibacterial action of silver is enhanced by
the presence of an electric field. 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.[38] 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 ZnO[39]
[edit] Radiation sterilizationMethods of sterilization exist using radiation
such as electron beams, X-rays, gamma rays, or subatomic particles.[40]
Gamma rays are very penetrating and are commonly used for sterilization of
disposable medical equipment, such as syringes, needles, cannulas 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).
Electron beam processing 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.
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 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 some plastics, such as polystyrene foam if
exposed for prolonged periods of time.
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.
Sterlization by irradiation with gamma rays may however in some cases affect
material properties.[41]
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).
[edit] 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
protein solutions in biological research. A filter with pore size 0.2 µ
;m 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.
Filters can be made of several different materials such as nitrocellulose or
polyethersulfone (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 sterility, the
filter membranes need testing for punctures made during or prior to use. For
best results, pharmaceutical sterile filtration is performed in a room with
highly filtered air.
[edit] Cleaning methods that do not achieve sterilizationThis is a brief
list of cleaning methods that may be thought to "kill germs" but do not
achieve sterilization.
Washing in a dishwasher: Dishwashers often only use hot tap water or heat
the water to between 49 and 60 °C (120 and 140 °F)[citation needed], which
is not hot enough to kill some bacteria on cooking or eating utensils.
Bathing can not sterilize skin, even using antibacterial soap.
Disinfectants (for non-living objects) or antiseptics (for living objects
such as skin) can kill or remove bacteria and viruses, but not all.
Pasteurization of food also kills some bacteria and viruses, but not all.
[edit] See alsoAsepsis
Antibacterial soap
Contamination control
Electron irradiation
Food Technology
Aseptic Processing
Food preservation
Food rheology
Food storage
Food and Bioprocess Technology
Food safety
Food microbiology
Food chemistry
Food packaging
Food Engineering
Pasteurization
Prion
[edit] ReferencesWHO - Infection Control Guidelines for Transmissible
Spongiform Encephalopathies. Retrieved Jul 10, 2010
[edit] Notes1.^ WHO Glossary
2.^ UCLA Dept. Epidemiology: Definitions
3.^ CDC-Guideline for Disinfection and Sterilization in Healthcare
Facilities, 2008 Prions, p. 100. Retrieved July 10, 2010
4.^ Molins, Ricardo A. (2001). Food irradiation: principles and applications
. Wiley-IEEE. p. 23. ISBN 9780471356349. http://books.google.com/?id=dkNQqbXY3loC&printsec=frontcover#v=onepage&q&f=false.
5.^ Brown, Amy Christian (2007). Understanding Food: Principles and
Preparation (3 ed.). Cengage Learning. p. 546. ISBN 9780495107453. http://books.google.com/?id=edPzm5KSMmYC&printsec=frontcover#v=onepage&q&f=false.
6.^ 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.
76, Suppl. 1 / Vol. 81, Suppl. 1/: 21. http://www.asas.org/jas/98meet/98df.pdf. Retrieved 2007-03-06.
7.^ Thiel, Theresa (1999). "http://www.umsl.edu/~microbes/pdf/tyndallization.pdf" (PDF). Science in the Real World. http://www.umsl.edu/~microbes/pdf/tyndallization.pdf. Retrieved 2007-03-06.
8.^ "– Alberta Health and Wellness". Health.gov.ab.ca. http://www.health.gov.ab.ca/resources/publications/PersonalServicesPt1.pdf. Retrieved 2010-06-25.
9.^ Dental Volume 1 - Dentist training manual for military dentists
10.^ a b Zadik Y, Peretz A (Apr 2008). "The effectiveness of glass bead
sterilizer in the dental practice". J Isr Dent Assoc 25 (2): 36–9. PMID
18780544.
11.^ http://www.CDC.gov/OralHealth/InfectionControl/faq/bead.htm 2008-09-11
12.^ "Substitute Sterilants under SNAP as of September 28, 2006" (PDF). http://www.epa.gov/Ozone/snap/sterilants/sterilants.pdf. Retrieved 2010-06-25.
13.^ "Sterilization/Aeration Equipment". Solutions.3m.com. http://solutions.3m.com/wps/portal/3M/en_US/MedicalSpecialties/devices/products/medical-sterilization/equipment/. Retrieved 2010-06-25.
14.^ "Unique solutions for infection control, sterile processing, SPD, and
sterilization: EtO Sterilization Solutions". SteriCert. http://www.stericert.com/eo/index.html. Retrieved 2010-06-25.
15.^ Micro-dose sterilization method
16.^ "IARC Vol 60" (PDF). http://monographs.iarc.fr/ENG/Monographs/vol60/volume60.pdf. Retrieved 2010-06-25.
17.^ a b "NIOSH: Documentation for Immediately Dangerous to Life or Health
Concentrations (IDLH) / NIOSH Chemical Listing and Documentation of Revised
IDLH Values (as of 3/1/95) - intridl4". Cdc.gov. http://www.cdc.gov/niosh/idlh/intridl4.html. Retrieved 2010-06-25.
18.^ "ATSDR - MMG: Ethylene Oxide". Atsdr.cdc.gov. 2007-09-24. http://www.atsdr.cdc.gov/MHMI/mmg137.html. Retrieved 2010-06-25.
19.^ "Hospital eTool: Central Supply Module". Osha.gov. http://www.osha.gov/SLTC/etools/hospital/central/central.html. Retrieved 2010-06-25.
20.^ "TSO3, Ozone Sterilization, Medical Instrument Sterilizer - News". Tso3
.com. 2008-01-03. http://www.tso3.com/en/news-events/news-tso3-gets-promising-223.php. Retrieved 2010-06-25.
21.^ "TSO3, Ozone Sterilization - Medical Instrument Sterilizer - Low-
Temperature Sterilization". Tso3.com. 2010-06-08. http://www.tso3.com. Retrieved 2010-06-25.
22.^ "OSH Answers: 1-Basic Information on Ozone". Ccohs.ca. 1999-02-19. http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/ozone/basic_ozo.html. Retrieved 2010-06-25.
23.^ Beth Israel Deaconess Medical Center Biosafety Manual (2004 edition)
24.^ Office of Health and Safety (2007). Biosafety in Microbiological and
Biomedical Laboratories (BMBL) (5th ed.). Centers for Disease Control and
Prevention. http://www.cdc.gov/OD/ohs/biosfty/bmbl5/bmbl5toc.htm.
25.^ "MAUDE - Manufacturer and User Facility Device Experience". Accessdata.
fda.gov. http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfMAUDE/search.CFM. Retrieved 2010-06-25.
26.^ "Occupational Safety and Health Guideline for Hydrogen Peroxide". Osha.
gov. http://www.osha.gov/SLTC/healthguidelines/hydrogenperoxide/recognition.html. Retrieved 2010-06-25.
27.^ "ATSDR - MMG: Hydrogen Peroxide". Atsdr.cdc.gov. 2007-09-24. http://www.atsdr.cdc.gov/MHMI/mmg174.html. Retrieved 2010-06-25.
28.^ 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. doi:10.1093/jac/
dkm006. PMID 17307768.
29.^ "Antibacterial effects of silver". http://www.saltlakemetals.com/Silver_Antibacterial.htm.
30.^ Chang TW, Weinstein L (December 1975). "Prevention of herpes
keratoconjunctivitis in rabbits by silver sulfadiazine". Antimicrob. Agents
Chemother. 8 (6): 677–8. PMC 429446. PMID 1211919. http://aac.asm.org/cgi/pmidlookup?view=long&pmid=1211919.
31.^ 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. doi:10.1016/j.burns.2006.06.010. PMID 17137719.
32.^ a b 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. doi
:10.1111/j.1365-2702.2007.02264.x. PMID 18705778.
33.^ Hermans MH (December 2006). "Silver-containing dressings and the need
for evidence". The American journal of nursing 106 (12): 60–8; quiz 68–9.
PMID 17133010.
34.^ "AGC Flat Glass Europe launches world’s first antibacterial glass".
2007-09-04. http://www.agc-flatglass.eu/AGC+Flat+Glass+Europe/English/Homepage/News/Press+room/Press-Detail-Page/page.aspx/979?pressitemid=1031.
35.^ "Samsung laundry featuring SilverCare Technology". Samsung. Archived
from the original on 2006-05-31. http://web.archive.org/web/20060531115914/http://www.samsung.com/PressCenter/PressRelease/PressRelease.asp?seq=20060213_0000233684. Retrieved 2007-08-06.
36.^ "Ultra-Fresh technology is based on the power of silver to fight
bacteria". Express Textile. http://www.expresstextile.com/20050731/perspectives01.shtml.
37.^ "FDA Clears Silver-Coated Breathing Tube For Marketing". 2007-11-08. http://www.fda.gov/bbs/topics/NEWS/2007/NEW01741.html. Retrieved 2007-11-11.
38.^ O. Akhavan and E. Ghaderi "Enhancement of antibacterial properties of
Ag nanorods by electric field" Sci. Technol. Adv. Mater. 10 (2009) 015003
free download
39.^ N. Padmavathy et al. "Enhanced bioactivity of ZnO nanoparticles—an
antimicrobial study" Sci. Technol. Adv. Mater. 9 (2007) 035004 free download
40.^ Trends in Radiation Sterilization of Health Care Products, IAEA, Vienna
,24 September 2008
41.^ Bharati, S; Soundrapandian C; Basu D; Datta S (2009). "Studies on a
novel bioactive glass and composite coating with hydroxyapatite on titanium
based alloys: Effect of γ-sterilization on coating". J Eur. Ceram. Soc. 29:
2527–35. doi:10.1016/j.jeurceramsoc.2009.02.013. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TX0-4VXCFXH-1&_user=1310866&_coverDate=09/30/2009&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1472314667&_rerunOrigin=scholar.google&_acct=C000052285&_version=1&_urlVersion=0&_userid=1310866&md5=fbcfe1db05e0d0b1cc2295124ac656ee&searchtype=a.
[edit] General referencesNinemeier J. Central Service Technical Manual (6th
ed.). International Association of Healthcare Central Service Materiel
Management. http://cbspd.net/cstechpub.htm.
Control of microbes
Raju GK, Cooney CL (1993). "Media and air sterilization". In Stephanopoulos
G. Biotechnology, 2E, Vol. 3, Bioprocessing. Weinheim: Wiley-VCH. pp. 157–
84. ISBN 3-527-28313-7. | k****i
发帖数: 1126 | 2 我正准备帮你贴这个呢，卡卡。
issues
【在 s**********8 的大作中提到】
: Sterilization (microbiology)
: http://en.wikipedia.org/wiki/Sterilization_(microbiology)
: From Wikipedia, the free encyclopediaJump to: navigation, search This
: article has multiple issues. Please help improve it or discuss these issues
: on the talk page.
: It may need reorganization to meet Wikipedia's quality standards. Tagged
: since March 2008.
: It is in need of attention from an expert on the subject. WikiProject
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: Contents [hide]
| k****i
发帖数: 1126 | 3 你贴过human factor 没有？
issues
【在 s**********8 的大作中提到】
: Sterilization (microbiology)
: http://en.wikipedia.org/wiki/Sterilization_(microbiology)
: From Wikipedia, the free encyclopediaJump to: navigation, search This
: article has multiple issues. Please help improve it or discuss these issues
: on the talk page.
: It may need reorganization to meet Wikipedia's quality standards. Tagged
: since March 2008.
: It is in need of attention from an expert on the subject. WikiProject
: Microbiology may be able to help recruit one. Tagged since December 2010.
: Contents [hide]
| s**********8
发帖数: 25265 | 4 no le. 你来.
【在 k****i 的大作中提到】
: 你贴过human factor 没有？
:
: issues
| a*i
发帖数: 1652 | 5 why not just post abstract or main points? Too long... | s**********8
发帖数: 25265 | 6 for GDP..
【在 a*i 的大作中提到】
: why not just post abstract or main points? Too long...
| A*D
发帖数: 116 | |
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