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 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

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

Disinfection The best agent and most enduring is Chlorine 1774 Chlorine discovered (Scheele) 1825 Chlorine used in sanitation Used by Oliver Wendell Holmes 1861 Used by Ignaz Semmelweiss Used by Dakin

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

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

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 : 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!

Disinfectants Factors affecting activity: 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 Stability Test Capacity Test Screening Test Rideal-Walker and Chick Martin Tests (phenolic coefficient is meaningless for a non- phenolic)

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. 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.