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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.

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Presentation on theme: "Disinfection. The best agent and most enduring is Chlorine 1774 Chlorine discovered (Scheele) 1825 Chlorine used in sanitation. 1843 Used by Oliver."— Presentation transcript:

1 Disinfection


3 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

4 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

5 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.

6 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

7 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

8 Disinfectants Alcoholsethanol isopropanol Aldehydesformaldehyde glutaraldehyde AmpholytesTego Pine fluidsJeypine HalogensChlorine, iodine (hypochlorites or NaDCC, chlorine dioxide, iodophors)

9 Disinfectsnts Phenolics Black fluids (Jeyes) White fluids (Izal) Clear soluble (Hycolin) Chloroxylenol (Dettol) Hexachlorophane (phisoHex) Anionic and non ionic detergents QAC’sBenzalkonium chloride (cationic detergents)Cetrimide (Cetavlon) Diguanides Chlorhexidine (Hibitane)

10 Disinfection

11 Disinfectants Antibiotics andDisinfectants Therapeutics In vivoIn vitro Act selectivelyNon-specific Require MetabolicDo not activity. Resistance is permanenttemporary

12 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

13 Disinfectants – Sites of action

14 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!

15 Disinfectants Factors affecting activity: Accessibility Temperature pH Concentration

16 Disinfectants Testing Control or ‘Buying and Selling’ tests must be reproducible. They are for Manufacturers in QC settling disputes and investigating potentials.

17 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 non- phenolic. The tests are unrepeatable in one lab and irreproducible between labs

18 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.

19 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 2 nd addition is good!

20 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.

21 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)

22 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.

23 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

24 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.

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