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8/4/2019 Disinfection Group 3
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Group 3
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Mosha Thadei cMnyazilu Albert
Mashaka KusekwaMakyao Mathias
Mboya Jackson
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Learning ObjectivesAt the end of this lecture, the student should be able
to
Define disinfection
Mode of action
Factors influencing antimicrobial activity
Describe the common substances and processes used to
achieve these outcomes Evaluate issues influencing choice of method
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Definitions
Cleaning process which physically removes contamination but does not
necessarily destroy micro-organisms
prerequisite before decontamination by disinfection or sterilisation ofinstruments
organic material prevents contact with microbes, inactivatesdisinfectants
Disinfection using an agent that destroys germs or other harmful microbes or
inactivates them, usually referred to chemicals that kill the growingforms (vegetative forms) but not the resistant spores of bacteria or
The reduction or elimination ofpathogenic microorganisms inor on materials, so they are no longer a health hazard.
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DefinitionsAntisepsis
destruction of pathogenic microorganisms existing intheir vegetative state on living tissue
Sterilization any process, physical or chemical, that will destroy all
forms of life, including bacterial, fungi, spores, andviruses
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Antimicrobial modes of action for
disinfectants and antiseptics damage the lipids and/or proteins of the semi permeable
cytoplasmic membrane of microorganisms resulting in
leakage of cellular materials needed to sustain life
denature microbial enzymes and other proteins by
disrupting the hydrogen and disulfide bonds
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Different categories of such
chemical agents Phenol and phenol derivatives
alter membrane permeability and denature proteins
chlorhexidine ineffective against endospores
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Factors Influencing Antimicrobial
Activity The concentration and kind of a chemical agent used;
The intensity and nature of a physical agent used;
The length of exposure to the agent;
The temperature at which the agent is used;
The number of microorganisms present;
The species or strain of microorganism;
The nature of the material bearing the microorganism;
The presence of organic or other interfering substances.
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Chemicals Use depends on spectrum
of antimicrobial activityand compatibility with
materials Also limited by dangers of
chemicals themselves
Examples Halogens
Alcohols
Alkylating agents Ethylene oxide
Phenolics
cetrimide (QAC)
chlorhexidine (diguanide)
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Halogens Hypochlorites (household
bleach) & chlorine
Advantages
active against viruses, spores,fungi
Disadvantages
inactivated by organic matter,freshness & pH critical (go off ifdiluted), corrosive to metals
Practical Uses 0.1% hypochlorite used as general
disinfectant
Strong hypochlorite (0.25%) used inlab & on wounds
Extra strong (1%) used on HBVblood spills
Chlorine used to treat drinkingwater and control Legionella
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Halogens Iodophors & iodine
Advantages Some activity against viruses, spores, fungi
denatures microbial proteins
effective against some endospore
Disadvantages inactivated by organic matter, can stain skin, irritant, expensive
Practical Uses Pre-op skin disinfection
Povidone iodine used as surgical scrub, as powder on ulcers
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Alcohols Isopropanol & ethanol
Advantages kill vegetative bacteria on clean surfaces in 30 seconds
Disadvantages inactive against spores, fungi
Inflammable
Need to be at correct %age with water (65-80%)
Practical uses Skin antisepsis before venepuncture Hand rubs
Disinfection of e.g. trolley tops
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Alkylating agents Glutaraldehyde and Formaldehyde
denature microbial proteins
glutaraldehyde: kill vegetative bacteria in 10-30 minutes andendospores in about 4 hours
Advantages Good activity against spores, virues, fungi
Disdvantages Glutaraldehyde only moderately active against TB Need long exposure time for full effect (3 hours) freshness & pH critical TOXIC!
Practical uses Disinfection of endoscopes Blood spills Fumigation
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Ethylene oxide Highly toxic flammable gas, kills spores!
Used for bulky items such as heart lung machines
Can be used on glutaraldehyde-labile endoscopes Use limited by safety issues
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Phenolics & QACs Clear soluble phenolics (e.g. Hycolin) used as
disinfectant on soiled surfaces, relatively inactiveagainst spores and viruses
Hexachlorophane used as surgical scrub
Quaternary ammonium compounds, e.g. cetrimideusually only used in combination with other agents;
good detergent properties.
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Chlorhexidine (a diguanide) Used as general purposeantiseptic for skin and mucousmembranes in manyformulations, e.g. Hibiscrub,Hibisol, Savlon
Advantages: relatively non-toxicand good against S. aureus
Disadvantages: can supportgrowth of e.g. P. aeruginosa
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Chlorine
Reacts with water to form hypochlorite ions, which in
turn denature microbial enzymes
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Factors determining usefulness of
chemical disinfection Spectrum of antimicrobial activity
is it the right agent for the job?
Used at correct concentration concept of 'in use concentration
diluted down from high concentration
stored for
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Factors determining usefulness of
chemical disinfection Time of exposure
You cannot disinfect an endoscope in 5 minutesglutaraldehyde!
Correct pH?
Inactivating materials
Pus, blood vomit, cork, soaps etc
Is disinfectant sterile? Many cases of Gram-negatives living in disinfectants!
Microbiological in-use testing
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Summary Definitions
Physical methods
heat (wet heat with pressure=autoclaving), filtration,irradiation
Chemical methods
Halogens, alkylating agents, EtOxide, alcohols, etc.
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References Seymour S. Block: Disinfection, sterilization and preservation
Williams &Wilkins (ISBN 0812113640) PIDAC best practices for cleaning, sterilization and disinfection
http://www.health.gov.on.ca/english/providers/program/infectious/diseases/best_prac/bp_cds_2.pdf
PIDAC best practices for environmental cleaninghttp://www.health.gov.on.ca/english/providers/program/infectious/diseases/best_prac/bp_enviro_clean.pdf
CDC guideline for disinfection and sterilization in healthcarefacilitieshttp://www.cdc.gov/hicpac/pdf/guidelines/Disinfection_Nov_2008.pdf
Bryce EA et al. When the biological indicator is positive: investigatingautoclave failures Infect Control Hosp Epi 1997;18:654-6
Rutala WA, Weber DJ. How to assess risk of disease transmission topatients when there is a failure to follow recommended disinfection andsterilization guidelines Infect Control Hosp Epidemiol. 2007;28(2):146-55
http://www.health.gov.on.ca/english/providers/program/infectious/diseases/best_prac/bp_enviro_clean.pdfhttp://www.health.gov.on.ca/english/providers/program/infectious/diseases/best_prac/bp_enviro_clean.pdfhttp://www.cdc.gov/hicpac/pdf/guidelines/Disinfection_Nov_2008.pdfhttp://www.cdc.gov/hicpac/pdf/guidelines/Disinfection_Nov_2008.pdfhttp://www.health.gov.on.ca/english/providers/program/infectious/diseases/best_prac/bp_enviro_clean.pdfhttp://www.health.gov.on.ca/english/providers/program/infectious/diseases/best_prac/bp_enviro_clean.pdf