Medical Microbiology

PrinciplesofSterilizationandDisinfection 39

ChemicalMethodsofSterilizationandDisinfection

Ethyleneoxide.Thishighlyreactivegas(C 2 H 4 O)isflammable,toxic,anda

strongmucosalirritant.Ethyleneoxidecanbeusedforsterilizationatlow

temperatures(20– 608 C).Thegashasahighpenetrationcapacityandcan

evengetthroughsomeplasticfoils.Onedrawbackisthatthisgascannot

killdriedmicroorganismsandrequiresarelativehumiditylevelof 40 –

90 %inthesterilizingchamber.Ethyleneoxidegoesintosolutioninplastics,

rubber,andsimilarmaterials,thereforesterilizeditemsmustbeallowedto

standforalongerperiodtoensurecompletedesorption.

Aldehydes.Formaldehyde(HCHO)isthemostimportantaldehyde.Itcanbe

usedinaspecialapparatusforgassterilization.Itsmainuse,however,isin

disinfection.Formaldehydeisawater-solublegas.Formalinisa 35 %solution

ofthisgasinwater.Formaldehydeirritatesmucosa;skincontactmayresultin

inflammationsorallergiceczemas.Formaldehydeisabroad-spectrumger-

micideforbacteria,fungi,andviruses.Athigherconcentrations,spores

arekilledaswell.Thissubstanceisusedtodisinfectsurfacesandobjects

in0.5– 5 %solutions.Inthepast,itwascommonlyusedingaseousformto

disinfecttheairinsiderooms(5g/m^3 ).Themechanismofactionofformal-

dehydeisbasedonproteindenaturation.

Anotheraldehydeusedfordisinfectionpurposesisglutaraldehyde.

Alcohols.Thetypesofalcoholusedindisinfectionareethanol(80%),propanol

(60%),andisopropanol(7 0 %).Alcoholsarequiteeffectiveagainstbacteriaand

fungi,lesssoagainstviruses.Theydonotkillbacterialspores.Duetotheir

rapidactionandgoodskinpenetration,themainareasofapplicationofal-

coholsaresurgicalandhygienicdisinfectionoftheskinandhands.Onedis-

advantageisthattheireffectisnotlong-lasting(nodepoteffect).Alcohols

denatureproteins.

Phenols.Listerwasthefirsttousephenol(carbolicacid)inmedicalapplica-

tions.Today,phenolderivativessubstitutedwithorganicgroupsand/orhalo-

gens(alkylated,arylated,andhalogenatedphenols),arewidelyused.One

commonfeatureofphenolicsubstancesistheirweakperformanceagainst

sporesandviruses.Phenolsdenatureproteins.Theybindtoorganicmaterials

toamoderatedegreeonly,makingthemsuitablefordisinfectionofexcreted

materials.

Halogens.Chlorine,iodine,andderivativesofthesehalogensaresuitablefor

useasdisinfectants.Chlorineandiodineshowageneralizedmicrobicidalef-

fectandalsokillspores.

Chlorinedenaturesproteinsbybindingtofreeaminogroups;hypochlo-

rousacid(HOCl),ontheotherhand,isproducedinaqueoussolutions,then

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Kayser, Medical Microbiology © 2005 Thieme