Disinfection

Disinfection

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

DisinfectionAntiseptics – 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.

DisinfectionThe 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 sensitiveMycobacteria - relatively resistantBacterial spores - extremely resistant Enveloped viruses – very sensitiveNon 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.1843 Used by Oliver Wendell Holmes1861 Used by Ignaz Semmelweiss1914-18 Used by Dakin

Disinfectants

Alcohols ethanol, isopropanolAldehydes formaldehyde glutaraldehydeAmpholytesTegoPine fluids JeypineHalogens chlorine, 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 detergentsQAC’s: Benzalkonium chloride(cationic detergents) Cetrimide (Cetavlon)Diguanides : Chlorhexidine (Hibitane)

Disinfection

DisinfectantsAntibiotics and DisinfectantsTherapeutics

In vivo In vitroAct selectively Non-specificRequire Metabolic Do notactivity.Resistance is Resistance ispermanent 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

DisinfectantsThe 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 possible3. 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.