Medical Microbiology

PrinciplesofSterilizationandDisinfection 37

bylight(photoreactivation).Mostchemicalagents(alcohols,phenols,alde-

hydes,heavymetals,oxidants)denatureproteinsirreversibly.Surfactant

compounds(amphotericandcationic)attackthecytoplasmicmembrane.

AcridinederivativesbindtoDNAtopreventitsreplicationandfunction(tran-

scription).

PhysicalMethodsofSterilizationandDisinfection

Heat

Theapplicationofheatisasimple,cheapandeffectivemethodofkilling

pathogens.Methodsofheatapplicationvaryaccordingtothespecificappli-

cation.

&Pasteurization.Thisistheantimicrobialtreatmentusedforfoodsinli-

quidform(milk):

— Low-temperaturepasteurization: 61 .5 8 C, 30 minutes; 718 C, 15 seconds.

— High-temperaturepasteurization:brief(seconds)ofexposureto 80 – 858 C

incontinuousoperation.

— Uperization:heatingto 1508 Cfor2.5secondsinapressurizedcontainer

usingsteaminjection.

&Disinfection.Applicationoftemperaturesbelowwhatwouldberequired

forsterilization.Important:boilingmedicalinstruments,needles,syringes,

etc.doesnotconstitutesterilization!Manybacterialsporesarenotkilled

bythismethod.

&Dryheatsterilization.Theguidelinevaluesforhot-airsterilizersareas

follows: 1808 Cfor 30 minutes, 1608 Cfor 120 minutes,wherebytheobjectsto

besterilizedmustthemselvesreachthesetemperaturesfortheentirepre-

scribedperiod.

&Moistheatsterilization.Autoclaveschargedwithsaturated,pressurized

steamareusedforthispurpose:

— 1218 C, 15 minutes,oneatmosphereofpressure(total: 202 kPa).

— 1348 C,threeminutes,twoatmospheresofpressure(total: 303 kPa).

Inpracticaloperation,theheatingandequalibriatingheatupandequalizing

timesmustbeaddedtothese,i.e.,thetimerequiredforthetemperaturein

themostinaccessiblepartoftheitem(s)tobesterilizedtoreachsterilization

level.Whensterilizingliquids,acoolingtimeisalsorequiredtoavoidboiling

pointretardation.

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Kayser, Medical Microbiology © 2005 Thieme