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Method of Disinfection

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					Universiti Teknologi MARA
               PHR 213


      Disinfection




                            By: C. H. Leow
     Definition
 • Disinfection:
- A process, which aims to reduce the number
  of pathogenic microorganisms in a particular
  situation.
- Destroy infective vegetative organism but not
  necessarily resistant spores.
- Often involves use of chemicals.
     Definition
• Disinfectants :
- Chemicals agents used to destroy harmful
  microorganism usually in inanimate objects.
        Definition
• Antiseptics :
   - Chemical agents usually applied to living
   tissue in humans / animals in order to destroy
   or prevent growth harmful microorganism -
   Often a lower concentration of agents used for
   disinfection.
         Definition
• Preservatives :
    - Describe a purpose of anti microbial agents in
      protecting medicine, pharmaceutical
      formulations etc. against microbial.
          General principles for
           disinfectant usage
• Disinfectants should be use if
    - Reduction in bacterial / viral load is needed
    - Disinfection by heat is impossible -
    Cleaning is insufficient
Usually applicable for
• Treatment of skin or mucous membrane •
Disinfection of instruments when physical
method cannot be used
• Making potentially inactive items safe for
  subsequent handling
• Decontaminations of surfaces
Disinfectant should NOT be used
 • Where sterility is necessary
 • Where heat treatment is possible • Where
 cleaning is sufficient • For storage of sterile
 instruments • As cleaning agents or
 deodorants • With a vague idea of making
 everything safe • To spray the air in an attempt
 to reduce cross infection
 • Because free samples given by somebody
Ideal properties of disinfectants
 • Safe, effective and selective
 • Germicidal
 • Wide spectrum of activity •
 Fast action and long lasting
 • Low development of resistant towards
   microorganism
 • Non-toxic to human
 • Do not cause local damage
 • Do not colorize, odorless
 • Low cost
Level of action of disinfectants
 Destruction of all microorganism
 High             but not necessarily resistant
                  spores

                  Destruction of all vegetative
 Intermediate
                  bacteria including M.
                 tuberculosis, may include virus or
                 fungi. Little / no sporicidal activity
                  Can destroy most vegetative
 Low
                 bacteria, virus, fungi. Does not
                 include spores
    Factors affecting choice of
       antimicrobial agents
• Properties of chemical agents
• Microbiological challenge •
Intended application •
Environmental factors • Toxicity
of agents
Properties of chemical agents
• Rate and extent of chemical reaction
  depends on
  - Concentration of chemicals
  - Temperature
- pH
  - Formulation -
  Tissue toxicity
Microbial challenge
• Outcome of chemical treatment depends
  on
  - Types of microorganism present -
  Level of microbial contamination -
  Intended application e.g. disinfectant,
  antiseptic OR preservative
  - Disinfectant for instruments - chemical must
    not have adverse effect on instrument e.g.
    corrosion of metals
Environmental Factors
  - Organic matters can decrease conc of active
  agents OR act as barrier to the disinfectant by
  adsorption or chemical inactivation - E.g: Blood,
  body fluids - decrease effectiveness of
  antimicrobial agents
Toxicity of agents
• Eg: phenolics, formaldehyde,
      glutaraldehyde
1. Aldehydes
      Aldehydes
• Powerful disinfectant against bacteria,
  fungi and many viruses
• Slow acting against spores
• Denatures protein
• Destroy vegetative cells & spores
• Glutaraldehyde

  - Non-corrosive to most materials - Use to
  sterile surgical instruments - To kill bacterial
  spores - soak instruments in glutaraldehyde
  for ≥ 10 hours
  - In cleaned instruments - immerse in solvent
    for 15 minutes
• Formaldehyde
   - Sporicidal effect  greatly with  in
     temperature

   - Solution
      • Disinfection of blankets & bedding
   - Gas
      • Use in sterilization with low temperature steam for
        heat sensitive items
2. Alcohols
        Alcohol
• Bactericidal but not sporicidal
• Poor penetration of organic matter - use
  restricted to clean condition
• Disinfection of skin & hard surfaces
            Alcohol
• Ethyl alcohol
   - Cleansing in pre-operative area of skin before
   injection at concentration of 60 - 70% - Use to 
   activity of other disinfectant preparation e.g:
   chlorhexidine
   - To kill 90 % of bacteria - wet skin surface with
     ethanol for 2 mins
            Alcohol
• Phenylethanol
   - Preservative in eye drop & contact lens
     solution
• Benzyl alcohol
  - Preservative in injections
• Phenoxyethanol
 - Antiseptic (against Pseudomonas aeruginosa)
3. Cationic surfactants
• Quaternary ammonium compound

  - Powerful cleansing agent - active at high
    dilution
  - Virtually non-toxic
  -  activity when use with benzyl alcohol -
  Incompatible with soaps, anionic surfactant,
  citrate
• Benzalkonium chloride
   - Usually used as skin antiseptic (solution for
     wounds and burns)
   - Preservatives in nard contact lens cleansing /
     soaking solution
   - Widely used in gynaecology and general
     surgery
   - Interferes with cell permeability  leakage of
      content  lysis
   - Aq soln susceptible to contamination; should
     be sterilized prep or freshly prepared
4. Biguanides
• Chlorhexidine
  - Active against a wide range of bacteria
  - Non-toxic antiseptic
  - Widely use in general disinfection alone or in
    combination with cetrimide
  - Chlorhexidine acetate / gluconate 0.5 % in
    ethanol 70 % - used for skin and hand
    disinfection
5. Phenolics
• Phenolics

- Most effective in acidic conditions
- At conc > 1% - bactericidal - At
conc < 1% - bacteriostatic - Little
activity against spores
• Chlorocresol
   - Bactericide in injection and preservative in oil-
     in-water creams
• Chloroxylenol
   - Use in skin & wound disinfection e.g: Dettol
• Phenols
   - Active against vegetative bacteria and fungi
   - Diluted to 1% w/v for lotion or gargles -
   Dissolved in glycerol for ear drop
6. Oxidizing agents
 • Hydrogen peroxide

 - H2O2 decomposes to form H2O & O2  -
 Antimicrobial effect by oxidizing cell material -
 Disinfection of soft contact lenses - Solution
 for wounds / ulcers & mouthwash - H2O2 ear
 drops use for removal of earwax - Should not
 be infected / instilled into close cavity  O2
 cannot escape
• Potassium permanganate

  - Bactericidal effect at 0.01%
  - As wound cleansing at 0.025% - 0.1%
  - Treatment of mycotic infection at 1% -
  Color the skin purple
7. Halogens and their
     compounds
• Hypochlorites

  - Chlorine releasing compounds
  - Disinfectant / household bleach (solution for
    surfaces % instruments)
  - Diluted - domestic hygiene e.g. Eusol
    (solution for skin & wounds)
  - High chemical reactivity, lethal to bacteria,
    fungi and viruses
  - Optimal activity at pH 5.0
• Iodine

 -Wide spectrum antimicrobial activity
 - Denature cell protein & essential enzymes
 - Staining of skin / fabrics
 - Possible sensitizing of skin
• Iodophors

   - Slow release of iodine
   - E.g: povidone-iodine
   -Treatment of contaminated wounds
   - Should remain in skin for 2 mins for antiseptic
   purposes
8. Heavy metals
          Mercury
• Phenylmercuric nitrate
  - Bactericide in eye drops and injections
• Thiomersal
  - Preservative in biological products and eye
    drops
                Silver
• Silver nitrates
- Injection of eyes


• Silver suphadiazine
- Prophyaxis in skin infection due to burns
9. Dyes
  • Acridines
- Slow acting, bacteriostatic

- Interferes specifically with nucleic acid
  formation

- E.g: proflavine, acriflavine

- Treatment of infected wounds & burns
          Pass Year Question
a) Define disinfectants, antiseptics and
   preservatives.                     (3 marks)

b) List THREE (3) properties of an ideal
                                     (3 marks)
   disinfectant.

c) State TWO (2) types of disinfectants and

   explain their uses.               (4 marks)

				
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Description: describe the technique of disinfection
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