3Disinfection The best agent and most enduring is Chlorine 1774 Chlorine discovered (Scheele)1825 Chlorine used in sanitation.1843 Used by Oliver Wendell Holmes1861 Used by Ignaz SemmelweissUsed by Dakin
4Disinfection 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, Sanitisationand decontamination
5DisinfectionAntiseptics – prevent growth or action of microorganisms and applied to living tissueLow level disinfectants - Most vegetative bacteria some fungi and some virusesIntermediate level disinfectants – TB Vegetative bacteria most viruses and fungiHigh level disinfectants - kill all microorganisms but not spores in less than 45min.Sterilants - Disinfectants that kill spores under certain conditions.Decontamination.
6DisinfectionThe 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
7Chemicals Some points : Gram positives - more sensitive Mycobacteria - relatively resistantBacterial spores - extremely resistantEnveloped viruses – very sensitiveNon enveloped viruses – more resistant.Prions - very resistant
11Disinfectants Antibiotics and Disinfectants Therapeutics In vivo In vitroAct selectively Non-specificRequire Metabolic Do notactivity.Resistance is Resistance ispermanent temporary
12Disinfectants 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
14Disinfectants The Ideal disinfectant : Has a broad spectrum of activity.Is bactericidal.Acts rapidlyDoes 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!
15Disinfectants Factors affecting activity: Accessibility Temperature pH Concentration
16Disinfectants Testing Control or ‘Buying and Selling’ tests must be reproducible. They are for Manufacturers in QC settling disputes and investigating potentials.
17Disinfectants 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 inappropriateR-W test does not include organic materialA phenolic coefficient is meaningless for a non-phenolic.The tests are unrepeatable in one lab and irreproducible between labs
18Disinfectants 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.
19Disinfectants Capacity Test : Disinfectant made up in hard water. Inoculum added at 10 min intervals (Ps.aer.+ or – yeast). Contact 8 mins0.02ml into 10ml recovery broth x5.No growth in 40% of broths after 2nd addition is good!
20Disinfectants 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.
21DisinfectantsThe 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)
22Disinfectants 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.
23Disinfection Disinfectant policy : Small Committee ! Define uses Eliminate use of chemicals where1. you aim to sterilise.2. use of heat is possible3 Where they are unnecessary
24Disinfection 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 supervisionIn-use testing on occasion.