Transcript Disinfection MSc

Disinfection
Disinfection
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
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
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.
Disinfection
The preferred method is moist heat – boiling or
pasteurisation between 65-80oC or steam at
subatmospheric pressure.
Where heating is impractical or impossible, where
cleaning is inadequate or for dealing with spills
or contamination with body fluids, chemicals
may be used.
In any case CLEANING is the first step
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
Disinfectants
Alcohols
Aldehydes
Ampholytes
Pine fluids
Halogens
ethanol isopropanol
formaldehyde
glutaraldehyde
Tego
Jeypine
Chlorine, iodine
(hypochlorites or NaDCC,
chlorine dioxide, iodophors)
Disinfectsnts
Phenolics
Black fluids
(Jeyes)
White fluids
(Izal)
Clear soluble
(Hycolin)
Chloroxylenol
(Dettol)
Hexachlorophane (phisoHex)
Anionic and non ionic detergents
QAC’s
Benzalkonium chloride
(cationic detergents) Cetrimide
(Cetavlon)
Diguanides
Chlorhexidine
(Hibitane)
Disinfection
Disinfectants
Antibiotics and
Therapeutics
In vivo
Act selectively
Require Metabolic
activity.
Resistance is
permanent
Disinfectants
In vitro
Non-specific
Do not
Resistance is
temporary
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
Disinfectants – Sites of action
Disinfectants
The Ideal
disinfectant :
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Is non toxic and leaves no toxic
residues.
Is easily used.
Deodorises.
Is colourless and non-staining.
Is non flammable.
Is soluble.
Is odourless.
Has a broad spectrum of activity.
Is bactericidal.
Acts rapidly
Does not deteriorate in storage.
Is persistent and stable.
Is not inactivated.
Is cheap.
In other words there is no ideal disinfectant!
Is non corrosive.
Disinfectants
Factors affecting activity:
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Accessibility
Temperature
pH
Concentration
Disinfectants
Testing
Control or ‘Buying and Selling’ tests must be
reproducible. They are for Manufacturers
in QC settling disputes and investigating
potentials.
Disinfectants
Rideal-Walker and Chick Martin Tests
Disinfectant is compared with a phenolic in its
ability to kill S. typhi. This is meaningless
because:
• Test org. is inappropriate
• R-W test does not include organic material
• A phenolic coefficient is meaningless for a nonphenolic.
• The tests are unrepeatable in one lab and
irreproducible between labs
Disinfectants
Stability Test :
Compares activity of a disinfectant in hard
water, fresh and 1 week old against a
strain of Ps. aeruginosa (NCTC 6749).
A starting concentration which kills the
organism whether fresh or old is
recommended for use.
Disinfectants
Capacity Test :
Disinfectant made up in hard water.
Inoculum added at 10 min intervals (Ps.aer.+
or – yeast). Contact 8 mins
0.02ml into 10ml recovery broth x5.
No growth in 40% of broths after 2nd addition
is good!
Disinfectants
Screening Test
Must be rapid. Used to select promising agents.
Eg MIC.
Beware the MIC is not a safe use dilution. It
involves unrealistic temperatures, times and
inocula. The MIC is not a concentration which
will inhibit bacterial growth under all conditions.
It is not a killing concentration and cannot
represent an in-use concentration. The survival
is measured in the presence of the disinfectant.
Disinfectants
The In-use Test – The only User’s 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 (= >500 orgs/ml)
Disinfectants
Neutralisers for In-Use test :
Nutrient Broth
Alcohols, Aldehydes, Hypochlorites and phenolics.
Nutrient Broth + Tween 80 (3%w/v)
Diguanides, hypochlorites+detergent, Iodophors,
Phenolic+detergent and QAC’s.
Disinfection
Disinfectant policy :
• Small Committee !
• Define uses
• Eliminate use of chemicals where
1. you aim to sterilise.
2. use of heat is possible
3 Where they are unnecessary
Disinfection
Disinfectant policy (cont’d)
• 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.