sterlization procedures and disinfection
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7/31/2019 Sterlization Procedures and Disinfection
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deepika m
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Decontamination
the process of removal of contaminatingpathogenic microorganisms from the
articles by a process of sterilization ordisinfection
use of physical or chemical means toremove, inactivate, or destroy living
organisms on a surface so that theorganisms are no longer infectious.
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Decontamination steps
CLEANING
STERLIZATION
STEAM DRY CHEMICAL
DISINFECTION
HIGH LEVELINTERMEDIATE
LEVELLOW LEVEL
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CLASSIFICATION OF INSTRUMENTSDEPINDING UPON ITS USE
CRITICAL
penetrate softtissue or bone,
enter thebloodstream ornormally sterile
tissue.
forceps, scalpels,bone chisels,scalers and
surgical burs
steam underpressure
(autoclaving), dryheat, or
heat/chemicalvapor
SEMICRITICALcontact mucousmembrane or
non-intact skin
mirrors,impression trays,amalgamcondensers,Endoscopes,Anesthesia
equipment
High leveldisinfection
NONCRITICALobjects thattouch onlyintact skin
x-ray heads,blood pressurecuffs and pulse
oximeters
Low leveldisinfection
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DISINFECTION Process of elimination of most pathogenic
microorganisms (excluding bacterial spores) oninanimate objects
Achieved by :-physical methods
chemical methods
STERLIZATION process where all the living microorganisms,
including bacterial spores are killed.Achieved by :-physical
chemical
physiochemical methods
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Classification of disinfectants:Based on consistency
Liquid (E.g., Alcohols, Phenols)
Gaseous (Formaldehyde vapor, Ethylene oxide)
Based on spectrum of activity
High level
Intermediate level Low level
Based on mechanism of action
Action on membrane (E.g., Alcohol, detergent)
Denaturation of cellular proteins (E.g., Alcohol, Phenol)
Oxidation of essential sulphydryl groups of enzymes (E.g.,H2O2, Halogens)
Alkylation of amino-, carboxyl- and hydroxyl group (E.g.,Ethylene Oxide, Formaldehyde)
Damage to nucleic acids (Ethylene Oxide, Formaldehyde)
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Chemical methods of disinfection
chemicals are known as disinfectants.
Properties :-
Should have wide spectrum of activity
ƒShould be able to destroy microbes within practical periodof time
ƒShould be active in the presence of organic matter
ƒShould make effective contact and be wettable
ƒShould be active in any pH
ƒShould be stable
ƒShould have long shelf life, high penetrating power ƒShould be non-toxic, non-allergenic, non-irritative or non-
corrosive
ƒShould not have bad odour
ƒShould not leave non-volatile residue or stain
ƒShould not be expensive and must be available easily
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High Level Disinfection (HLD)
There are three types of HLD:
Disinfection by boiling
Moist heat at 70-100°C
Chemical disinfection by:-Ethylene Oxide,
Gluteraldehyde,
Formaldehyde
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Low level disinfection by:-
Alcohols,
quaternary ammonium compounds
Intermediate level disinfectionby:-
Phenolics
halogens
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Mechanism of action
ALCOHOLS:
Mode of action: Alcohols dehydrate cells, disruptmembranes and cause coagulation of protein.
Examples: 70% Ethyl alcohol, isopropyl alcohol andmethyl alcohol
Uses:disinfect surfaces
clinical thermometers
methyl alc kills spores
Disadvantages: Skin irritant, volatile (evaporatesrapidly), inflammable
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ALDEHYDES:
Mode of action: Acts through alkylation of amino-,carboxyl- or hydroxyl group, and probably
damages nucleic acids. It kills all microorganisms,
including spores.
Examples: Formaldehyde, Gluteraldehyde
Uses :40% Formaldehyde (formalin) is used for
surface disinfection and fumigation of rooms,
chambers, operation theatres, biological safety
cabinets, wards, sick rooms etc
Disadv : Vapors are irritating, has poor penetration,
leaves non-volatile residue, activity is reduced in
the presence of protein
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PHENOLS
act as disinfectants at high concentration and as
antiseptics at low concentrations used to prevent infection of surgical wound
Disadv:toxic, corrosive and skin irritant.
HALOGENS
Iodophores permit slow release and reduce the irritationof the antiseptic.
For hand washing iodophores are diluted in 50%alcohol.
10% Povidone Iodine is used undiluted in pre andpostoperative skin disinfection
Disadv: Rapidly inactivated in the presence of organicmatter.
Iodine is corrosive and staining.
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HYDROGEN PEROXIDE:
Mode of action: acts on the microorganisms
through its release of nascent oxygen.Produces
hydroxyl-free radical that damages proteins and
DNA.
Application: It is used at 6% concentration to
decontaminate the instrumentes for 20 – 30 min,
equipments such as ventilators. 3%
Hydrogen Peroxide Solution is used for skin
disinfection and deodorising wounds and ulcers.
Strong solutions are sporicidal.
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HLD BY BOILING
best achieved by moist heat such as boiling in water
(100°C for one minute holding time)
kills all organisms
except for a few bacterial spores. note that boiling equipment items in water will not
achieve sterilization.
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STERLIZATION METHODS
STERLIZATION
PHYSICAL
SUNLIGHT HEAT VIBRATION RADIATION FILTRTION
CHEMICALPHYSIOCHEM
ICAL
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HEAT
DRY HEAT
RED HEAT
FLAMING
INCENERATION
HOT AIR OVEN
INFRARED
MOIST HEAT
BELOW 100DEGREE
AT 100
ABOVE 100
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DRY HEAT: Red heat : Articles such as bacteriological
loops, straight wires, tips of forceps andsearing spatulas holding them inBunsen flame become red hot.
This is a simple method for effectivesterilization
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Flaming:
Passing the article over a Bunsen flame, but notheating it to redness.
Articles such as scalpels, mouth of test tubes, flasks,glass slides and cover slips are passed through theflame a few times.
Most vegetative cells are killed, there is no guaranteethat spores too would die on such short exposure.
This method too is limited to those articles that can be
exposed to flame. Cracking of the glassware mayoccur.
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Incineration:
Method of destroying contaminated material by
burning them in incinerator.
Articles such as soiled dressings; animal carcasses,
pathological material and bedding etc should be
subjected to incineration.
This technique results in the loss of the article, hence is
suitable only for those articles that have to be disposed.
Burning of polystyrene materials emits dense smoke,
and hence they should not be incinerated.
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Hot air oven:
Introduced by Louis Pasteur.
Articles to be sterilized are exposed to high
temperature (160C) for duration of one hour in
an electrically heated oven.
Articles sterilized: Metallic instruments (like
forceps, scalpels, scissors), glasswares (such as
petri-dishes, pipettes, flasks, all-glass syringes),swabs, oils, grease, petroleum jelly and some
pharmaceutical products.
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Sterilization process:
Articles to be sterilized must be perfectly dry before
placing them inside to avoid breakage. Articles must be placed at sufficient distance so as to
allow free circulation of air in between
Sterlization cycle
60 minutes at 160C 40 minutes at 170C
20 minutes at 180C.
Increasing temperature by 10 degrees shortens thesterilizing time by 50 percent.
The hot air oven must not be opened until thetemperature inside has fallen below 60C to preventbreakage of glasswares.
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Advantages: It is an effective method of sterilization
of heat stable articles. The articles remain dry after
sterilization.
This is the only method of sterilizing oils and
powders.
Disadvantages:
ƒSince air is poor conductor of heat, hot air has
poor penetration.
ƒCotton wool and paper may get slightly charred. ƒGlasses may become smoky.
ƒTakes longer time compared to autoclave.
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Infra red rays: Brings sterilization by generation of heat
Articles to be sterilized are placed in a movingconveyer belt and passed through a tunnel that isheated by infrared radiators to a temperature of 180C.
The articles are exposed to that temperature for aperiod of 7.5 minutes.
Articles sterilized included metallic instruments andglassware. It is mainly used in central sterile supplydepartment
Not applicable in diagnostic laboratory
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Moist heat
Destroys through irreversible coagulationof proteins
Moist heat includes
BoilingPasteurization
Pressurized steam
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Boiling (100 C)
Destroys most microorganisms and viruses
Not effective means of sterilization
Does not destroy endospores
Pasteurization(below 100deg)
Pasteur developed to avoid spoilage of wine
Does not sterilize but significantly reduces organisms
Used to increase shelf life of food
Most protocols employ HTST method,Heated to 72°C
and held for 15 seconds Other protocol UHT(ultra high temp)Heated to 140°C -
150°C, held for several seconds then rapidly cooled
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Pressurized steam(above100deg)
Autoclave used to sterilize usingpressurized steam
Heated wate steamincreased pressure
Preferred method of sterilization Achieves sterilization at 121°C
and 15lbs in 15 minutes
Effective against endospores
Flash autoclaving sterilizes at
135°C and 15lbs in 3 minutes Prions destroyed at 132°C and
15lbs for 4.5 hours
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Other Physical Methods
of ControlHeat sensitive materials require other methods of
microbial control
Filtration
Irradiation
High-pressure treatment
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Filtration
Membrane filtration
used to remove microbes from fluids and air
Liquid filtration
Used for heat sensitive fluids
Membrane filters allow liquids to flow through
Traps microbes on filter Depth filters trap microbes using electrical charge
Filtration of air
High efficiency particulate air (HEPA) filter removenearly all microbes from air
Filter has 0.3µm pores to trap organisms
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Radiation
Electromagnetic radiation
Energy released from waves Based on wavelength and frequency
Shorter wavelength, higher frequency = more
energy
Range of wavelength is electromagnetic spectrum Radiation can be ionizing or non-ionizing
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Ionizing radiation
Radiation able to strip electrons from atoms
Three sources
Gamma radiation
X-rays
Electron accelerators
Causes damage to DNA and potentially to plasmamembrane
Used to sterilize heat resistant materials
Medical equipment, surgical supplies,
medications Some endospores can be resistant
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Non-ionizing radiation
Ultraviolet radiation
Only type to destroy microbes directly
Damages DNA
Causes thymine dimersUsed to destroy microbes in air, drinking water
and surfaces
Limitation
Poor penetrating powerThin films or coverings can limit effect
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High pressure processing
Used in pasteurization of commercial foods
Does not use high temperatures
Employs high pressureUp to 130,000 psi
Destroys microbes by denaturing proteins and
altering cell membrane permeability
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Sterlization control
Three methods exist to check the efficacy of
sterilization process
Physical
Chemical Biological.
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ƒPhysical: Temperature chart recorder andthermocouple.
ƒChemical: Browne’s tube No.3 (green spot,color changes from red to green)
ƒBiological: 10^6 spores of Bacillus subtilisvar niger or Clostridium tetani on paper stripsare placed inside
envelopes and then placed inside the hot airoven.Upon completion of sterilization cycle, the
strips are
removed and inoculated into thioglycollate brothor cooked meat medium and incubated at 37Cfor 3-5 days. Proper sterilization should kill the
spores and there should not be any growth.
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SummaryDisinfection and sterilization guidelines must be
followed to prevent exposure to pathogens that
may lead to infection
Delivery of sterile products for use in patient care
depends not only on the effectiveness of the
sterilization process but also on cleaning,
disassembling and packaging of the device,
loading and monitoring the sterilizer
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