disinfection group 3

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

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