Disinfection

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Disinfection
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Disinfection
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Disinfection

• The removal of harmful organisms
• (but not usually spores) or the reduction of
  numbers of organisms to a level where they are
  not harmful.
• Cf Sterilisation, Sanitisation
• and Decontamination

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Disinfection

• Antiseptics prevent growth or action of
  microorganisms and applied to living tissue
• Low level disinfectants - Most vegetative
  bacteria some fungi and some viruses
• Intermediate level disinfectants TB Vegetative
  bacteria most viruses and fungi
• High level disinfectants - kill all
  microorganisms but not spores in less than 45min.
• Sterilants - Disinfectants that kill spores under
  certain conditions.
• Decontamination.

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Disinfection

• The preferred method is moist heat boiling or
  pasteurisation between 65-80oC or steam at
  sub-atmospheric pressure.
• Chemicals may be used
• Where heating is impractical or impossible
• where cleaning is inadequate
• or for dealing with spills or contamination with
  body fluids
• In any case CLEANING is the first step

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Chemicals

• Some points
• Gram positives - more sensitive
• Mycobacteria - relatively resistant
• Bacterial spores - extremely resistant
• Enveloped viruses very sensitive
• Non enveloped viruses more resistant.
• Prions - very resistant

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Disinfection

• The best agent and most enduring is Chlorine
• 1774 Chlorine discovered (Scheele)
• 1825 Chlorine used in sanitation.
• 1843 Used by Oliver Wendell Holmes
• 1861 Used by Ignaz Semmelweiss
• 1914-18 Used by Dakin

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Disinfectants

• Alcohols ethanol, isopropanol
• Aldehydes formaldehyde glutaraldehyde
• Ampholytes Tego
• Pine fluids Jeypine
• Halogens chlorine, iodine (hypochlorites or
  NaDCC,
• chlorine dioxide, iodophors)

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Disinfectants

• Phenolics Black fluids (Jeyes)
• White fluids (Izal)
• Clear soluble (Hycolin)
• Chloroxylenol (Dettol)
• Hexachlorophane (phisoHex)
• Anionic and non ionic detergents
• QACs Benzalkonium chloride
• (cationic detergents) Cetrimide (Cetavlon)
• Diguanides Chlorhexidine (Hibitane)

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Disinfection
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Disinfectants

• Antibiotics and Disinfectants
• Therapeutics
• In vivo In vitro
• Act selectively Non-specific
• Require Metabolic Do not
• activity.
• Resistance is Resistance is
• permanent temporary

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Disinfectants

• Two basic mechanisms
• Solution of lipids from cell membrane by
  detergents and lipid solvents.
• Irreversible alteration of proteins eg by
  denaturants, oxidants, alkylating agents and
  sulphydryl agents

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Disinfectants Sites of action
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Disinfectants

• The Ideal disinfectant
• Has a broad spectrum of activity.
• Is bactericidal.
• Acts rapidly
• Does not deteriorate in storage.
• Is persistent and stable.
• Is not inactivated.
• Is cheap.
• Is non corrosive.

• Is non toxic and leaves no toxic residues.
• Is easily used.
• Deodorises.
• Is colourless and non-staining.
• Is non flammable.
• Is soluble.
• Is odourless.

In other words there is no ideal disinfectant!
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Disinfectants

• Factors affecting activity
• Accessibility
• Temperature
• pH
• Concentration

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Disinfectants

• Testing
• Control or Buying and Selling tests must be
  reproducible. They are for Manufacturers in QC,
  settling disputes and investigating potentials.

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Disinfectants

• Stability Test
• Capacity Test
• Screening Test
• Rideal-Walker and Chick Martin Tests
• (phenolic coefficient is meaningless for a
  non-phenolic)

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Disinfectants

• The In-use Test The only Users test for
  monitoring performance of an agent.
• Dilute disinfectant (1ml) in 9ml of diluent.
  Place ten drops (0.02ml) on a NA plate Incubate
  at 37 and RT for up to a week.
• Growth on either plate shows survival of orgs.
  More than 10 cols from each of 10 drops failure
  ( gt500 orgs/ml)

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Disinfectants

• Neutralisers for In-Use test
• Nutrient Broth
• Alcohols, Aldehydes, Hypochlorites and phenolics.
• Nutrient Broth Tween 80 (3w/v)
• Diguanides, hypochloritesdetergent, Iodophors,
  Phenolicdetergent and QACs.

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Disinfection

• Disinfectant policy
• Small Committee !
• Define uses
• Eliminate use of chemicals where
• 1. you aim to sterilise.
• 2. use of heat is possible
• 3. they are unnecessary

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Disinfection

• Disinfectant policy (contd)
• Choose and use according to recommendations of an
  independent body not a salesman.
• Distribute frequently and in correct dilutions
  (Preferably by pharmacist)
• Instruction and supervision
• In-use testing on occasion.