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Principle of Sterilization and Disinfectants 2007
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5/28/2018 Principle of Sterilization and Disinfectants 2007
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Principle of sterilization anddisinfections
Dr Habsah Hasan
Department of MedicalMicrobiology and Parasitology
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Introduction Infectious disease agents are controlled
by:
Public sanitation measures
Sterilization and disinfection procedures
Chemotherapeutic agents
Bodys defense mechanisms
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Terminology Sterilizationis the complete elimination or
destruction of all forms of microbial life. accomplished in health care facilities by either
physical or chemical processes. Disinfection: process that eliminates many
or all pathogenic microorganisms oninanimate objects, with the exception of
bacterial spores. Disinfection is usually accomplished by the use of
liquid chemicals or wet pasteurization in healthcare settings.
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Terminology When chemicals are used for the purposes of
destroying all forms of microbiologic life,
including fungal and bacterial spores, theymay be called chemical sterilants.
These same germicides used for shorterexposure periods may also be part of the
disinfection process (i.e., high-leveldisinfection).
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TerminologyAntiseptics- disinfectant agents that can
be used on body surfaces, such as skin
or vaginal tract, to reduce the numberof normal flora and pathogeniccontaminants
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Asepsis Processes designed to
prevent microorganismsfrom reaching aprotected environment.
E.g: for proceduresused in
the operating room
the preparation oftherapeutic agents, and
technical manipulation inthe microbiology lab
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Factors influencing efficacy Prior cleaning of the object;
Presence of organic and inorganic load
Type and level of microbial contamination
Concentration of and exposure time to the germicide
The nature of the object (e.g., crevices, hinges, andlumens)
Presence of biofilms
Temperature and pH of the disinfection process
Relative humidity of the sterilizationprocess (e.g.,with ETO).
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Organic materials Organic material (pus, blood, saliva,
urine and feces) protects organisms
from disinfection Hepatitis B virus in organic matter such as
dry blood - resistance to disinfectant
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Resistance organisms Bacterial endospores Most resistance forms
Able to stand 16 hours of boiling
Mycobacteria Cell surface is rich in wax-like lipids causing
resistance to disinfectant but sensitive to heat
Hepatitis virus and HIV Non culturable organismsunable to check post
disinfectants viability
Pseudomonasspp Proliferate in distilled and deionized water
Produce slime that is a barrier to disinfectants.
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MethodsPhysical Chemical methods
Heat
Filtration
Radiation
Phenols and phenolics
Alcohols
Halogens
Surfactants
Alkylating agents
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Heat
Moist heat Dry Heat
boiling
Steam under
atmospheric pressure
Steam under
atmospheric pressure
pasteurization
Dry heat sterilization
incineration
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Steam at atmospheric pressure
Steam contains latent heat generated duringvaporization
The latent heat is released when steamcondenses on a colder surface
The condensation release heat and moisturewhich is necessary for protein coagulation to
occur The shrinking of volume of the steam during
condensation creates a negative pressuredrawing in more steam
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Steam under pressure-
Autoclaving To obtain a moist heat temperature of 121 C,
saturated steam is placed under pressure of15 lbs per square inch and sterilizationachieved after 15 minutes
The required time of exposure diminished asthe temperature increased126C10 mins
Sterilization indicator chemical changes
Chemical imprinted on tapes and wrappers
culture testing for spores Bacillus stearothermophilus impregnated in ampoules or
filter paper strips
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Pasteurization Utilizes mild heat to destroy pathogenic
vegetative forms in liquids without alteringthe liquids palatibility
Used in cows to prevent infectious diseaseassociated with raw milktuberculosis,brucellosis, Camylopbacteriosis, dysentry, Qfever
Two methods Holding/Batch method
Milk in vessels is pasturised at 620C for 30 minutes
Flash/continuous flow method Thin films of milk stream over pipe or plates held at 71.7
C for 15 seconds.
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Moist HeatOrganisms Temperature Time
Most vegetative form of bacteria,yeast and mould, viruses
600C 30 minutes
Most vegetative form of bacteria,yeast and mould, viruses
800C 5 to 10minutes
Mould spores 800C 30
minutesBacterial spores 121 15 mins
Comparison of various conditions required to kill Microorganisms
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Methods sporocidal disinfection sterilization
Boiling x X
Steam(atmosphericpressure)
x X
Steam(under pressure)
NA
Pateurization X X
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Heat
Moist heat Dry Heat
boiling
Steam under
atmospheric pressure
Steam under
atmospheric pressure
pasteurization
Dry heat sterilization
incineration
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Dry heat Biomolecules exhibit less
thermosensitivity to dry heat than to
moist heat Dry heat is slower and requires
temperatures higher than those used in
moist heat
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Dry heat sterilization Used at 1600C for 2 hours or 1700C for 1 hour
Dry heat temperature below 1400C do not
destroy spores within a reasonable timeperiod.
Mechanically convected ovens are used forevenly distributed heat
Method of choice for sterilizing powders, oils,and thermostable materials that are adverselyaffected by moisture
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Incineration Used for discardable,combustible items
such as mask, gloves and wipes that
are soilde with blood and body fluid Flaming is a convenient way to
sterilized inexpensive heat tolerant
implements
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MethodsPhysical Chemical methods
Heat
Filtration
Radiation
Phenols and phenolics
Alcohols
Halogens
Surfactants
Alkylating agents
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Filtration Porous material to remove organisms
Applications of filters
Sterilization of liquids and air
Separation of microorganisms of differentsizes
Preparation of cell-free solutions of toxins,antigens
Determination of virus size
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Membrane filters Paper thin,sieve like elements composed of inert
cellulose esters
Pore size range differs (0.005 to 1 m) Pore size of 0.2 micron able to filter bacteria
Filters can be visualized under microscope or cultured
E.g High efficiency particulate air filters (HEPA) filters to filter
particles in the air Reduce particles as small as 0.3 micron with 99.97%
Sterilized serum
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MethodsPhysical Chemical methods
Heat
Filtration
Radiation
Phenols and phenolics
Alcohols
Halogens
Surfactants
Alkylating agents
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Radiation Ultraviolet radiation
Ionizing radiation
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Ultraviolet radiation Causes damage to DNA of the microorganisms
UV lamps- generate UV rays with wavelenth 240nmto 280nm
Application- to reduce microorganisms in air andsurfaces of hospital rooms, operating rooms,entryways, nurseries, gymnasium and cafaterias.
Problems-
Low penetrability. Organisms must be directly exposed to UV Overexposure to UV in human, causes skin erythema and
conjunctivitis
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Ionizing radiation Cobalt 60 produces cathode rays and gamma
rays
Advantage Avoid heat and moist
Allows prepackaging and sealing of items to besterilized
Application Sterilizing pharmaceuticals and disposable medical
supplies such as syringes and catheters.
Disadvantagefabrics tensile strength will be
reduced after irradiation
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MethodsPhysical Chemical methods
Heat
Filtration
Radiation
Phenols and phenolics
Alcohols
Halogens
Surfactants
Alkylating agents
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Chemical methods All chemicals used in sterilization and
disinfection are grouped as disinfectants.
Chemicals used for sterilization (underprescribed condition) are called sterilants orchemosterilizers
Chemical sterilants include Ethylene oxide (ETO) Formaldehyde and glutaryldehyde
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Ideal properties of disinfectant Able to destroy all forms of microorganisms
within practical period
Soil will not interfere with its reaction Nonirritating, non allergenic and non toxic
Non corrosive and non discolouring
Demonstrate wettability and penetrability
Soluble in water Chemically stable
Dilution will not adversely affect its activity
Do not have disagreeable odour or expensive
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Non of disinfectants meets all thequalification
Disinfection must be chosen on thebasis of their intrinsic properties and jobat hand.
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Classes of disinfectants Phenol and phenolics
Alcohols
Halogens
Surfactants
Alkylating agents
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Phenols and phenolics Properties:
have active compounds in the presence of organic matter
Stable and persist on surface for a long period. Inactivated by rubber, wood and plastics
Use: disinfecting saliva, feces and similar matter
Disadvantage: irritant to skin,
Diphenyl compounds used as skin disinfectant:hexachlorophene and chlorhexidine
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Chlorhexidine Greater bactericidal activity than
hexacholorophene
4% chlorhexidine used for surgical scrub,hand washing and wound cleansing
Persist on the skin, non irritating, notabsorbed
Action is neutralized by soaps and anionicdetergents
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Alcohols Contact time is important for action
Properties:
High antimicrobial properties on environmentalsurfaces
Use: skin and surface disinfectants
Disadvantage: Dilution reduce the
effectiveness, volatile, flammable and irritatesskin
Examples: Ethyl and isopropylalcohol70%
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Halogens Examples: Chlorine and iodine
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Chlorine Use: sanitation, purification and disinfection.
Elemental chlorinewater purification
Hypochloritesanitizing agents Concentration:
Less than 1 ppm- lethal to most vegetativebacteria, inactivates most viruses
5% sodium hypochloritesurface and glasswaredecontamination
Disadvantage:organic matters interfere withits activities
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Iodine Active compound: tincture of 2% in 50% alcohol Use:
wound and skin antisepsis
Preoperative skin antisepsis General disinfectants for thermometers and surgical
appliances
Disadvantage: cause tissue necrosis in strong concentration Stain skin
Povidone iodine has less tissue necrosis because theiodine is solubilized in povidone which provide asustained released of iodine
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Surfactants Examples
Anionic detergents (Soaps)
effective cleansers, little direct antibacterial effect Cationic detergents (quartenary ammonium
compounds)
highly bactericidal, inactive against spores and virus
Adsorbed into cotton, cork, dustbecomes inactive
Little toxicity to skin and mucous membrane
E.g. benzalkonium chloride
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Alkylating agents Formaldehyde
Glutaryldehyde
Ethylene oxide
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Formaldehyde Use:
gas state as fumigants to decontaminate
room or laboratory that have beenaccidentally and extensively contaminatedwith pathogenic bacteria
Liquid as formalin
Disadvantage: tissue irritant
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Glutaryldehyde Activity: wide spectrum. 2% solution is
bactericidal, tuberculocidal and virucidal in 10to 90 minutes, sporocidals in 10 hours
Effective sterilizing agent for apparatus thatcannot be heat treated such as lensinstrument, equipment for respiratory therapy
Disadvantage: not use as skin antisepsisbecause irritation to skin and soft tissue.
Commercially available: cidex
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Ethylene oxide Cyclic ether
Advantage: It can sterilized without high level
of heat and moisture Usage: catheters, disposable medical items,
dental handpieces, sutures
Disadvantage: toxic if inhaled, vesicant on
contact, slow acting, require 4 hours at 50 to56 C or 6 to 12 hours at room temperature toproduce sterility
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Vegetativebacteria
Fungi envelopedvirus
Non-enveloped virus Mycobacteria Bacterial spores
Phenol andphenolics
X X
Alcohols +/- X
Iodine
Chlorine X
Chlorhexidine 4%
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Vegetativebacteria
Fungi envelopedvirus
Non-enveloped virus Mycobacteria Bacterial spores
Quartenaryammoniumcompound
+/- X X X
Formaldehyde
Glutaryldehyde (2%)
(10-90 mins)
(10-90
mins)
(10-90
mins)
(10-90 mins)
(10-90
mins)
(10 hours)
Ethyleneoxide
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Disinfectant High-level disinfectants -At similar concentrations
with chemical sterilants but with shorter exposureperiods (e.g., 20 minutes for 2% glutaraldehyde),these same disinfectants will kill all microorganismswith the exception of large numbers of bacterialspores
Low-level disinfectantsmay kill most vegetativebacteria, some fungi, and some viruses in a practicalperiod of time (
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Mode of actionMoist Heat Coagulation of protein of the
microorganism, death- inactivationof enzymes, changes in nucleicacids and cytoplasm
Dry heat Alteration of protein by oxidation,desiccation and changes of osmoticpressure
Filtration Porous material to remove
organisms
Radiation damage to DNA of themicroorganisms
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STERILIZATION AND DISINFECTION TECHNIQUES COMMONLY USED IN HOSPITAL PRACTICE
Objective Method Principle of microbialinactivation Example of use
Sterilization
Steam autoclaving Thermal denaturation Metallic surgical instrumentsEthylene oxide Thermochemical denaturation Heat-labile surgicalinstruments
Gamma-irradiation Ionizing denaturation Implantable medical devices(catheters, protheses)Gas plasma Generated free radicalinduced denaturation Heat-labile instruments
Disinfection
Chlorine Chemical denaturation Water disinfectionAlcohols Chemical denaturation Skin antisepsisIodophors Chemical denaturation Skin and mucosae antisepsisAldehydes Chemical denaturation Flexible endoscopesPeracetic acid Chemical denaturation Flexible endoscopes
Common sterilization technique
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Common sterilization techniqueA: Heat sterilization, including steam or hot air (steam sterilizationprocessing time
from 3 to 30 minutes).B: Ethylene oxide gas ( generally 1 to 6 hours processing time plus aeration time of 8
to 12 hours at 50to 60C).C: Hydrogen peroxide gas plasma (Processing time between 45 and 72 minutes; for
endoscope or medical device restrictions based on lumen internal diameter and
length)D: Glutaraldehyde-based formulations (> 2% glutaraldehyde; caution should beexercised with all glutaraldehyde formulations when further in-use dilution is
anticipated); glutaraldehyde (0.95%) and 1.64% phenol/phenate. One
glutaraldehyde-based product has a 5 minute exposure time at 35C.E: Ortho-phthalaldehyde 0.55% (FDA cleared as high-level disinfectant; passes the
Sporicidal Activity Test in 32 hours at 20C but not cleared as a chemical
sterilant).F: Hydrogen peroxide 7.5% (will corrode copper, zinc, and brass).G: Peracetic acid; concentration variable but 1% or less is sporicidal. Peracetic acid
immersion system operates at 50to 56C.H: Hydrogen peroxide (7.35%) and 0.23% peracetic acid; hydrogen peroxide 1% and
peracetic acid 0.08% (will corrode metal instruments).