Medical Microbiology

1 GeneralAspectsofMedical

Microbiology

F.H.Kayser

&Infectiousdiseasesarecausedbysubcellularinfectiousentities(prions,

viruses),prokaryoticbacteria,eukaryoticfungiandprotozoans,metazoanan-

imals,suchasparasiticworms(helminths),andsomearthropods.Definitive

proofthatoneofthesefactorsisthecauseofagiveninfectionisdemon-

stratedbyfulfillmentofthethreeHenle-Kochpostulates.Fortechnicalrea-

sons,anumberofinfectionscannotfulfillthepostulatesintheirstrictest

senseasformulatedbyR.Koch,inthesecasesamodifiedformofthepos-

tulatesisapplied. &

TheHistoryofInfectiousDiseases

ThePast.....................................................

Infectiousdiseaseshavebeenknownforthousandsofyears,althoughaccu-

rateinformationontheiretiologyhasonlybeenavailableforaboutacentury.

InthemedicalteachingsofHippocrates,thecauseofinfectionsoccurringfre-

quentlyinacertainlocalityorduringacertainperiod(epidemics)wassought

in“changes”intheairaccordingtothetheoryofmiasmas.Thisconcept,still

reflectedintermssuchas“swampfever”or“malaria,”wasthepredominant

academicopinionuntiltheendofthe 19 thcentury,despitethefactthatthe

DutchclothmerchantA.vanLeeuwenhoekhadseenanddescribedbacteria

asearlyasthe 17 thcentury,usingamicroscopehebuilthimselfwithasingle

convexlensandaveryshortfocallength.Atthetime,generalacceptanceof

thenotionof“spontaneousgeneration”—creationoflifefromdeadorganic

material—stoodinthewayofimplicatingthebacteriafoundinthecorpses

ofinfectionvictimsasthecauseofthedeadlydiseases.ItwasnotuntilPas-

teurdisprovedthedoctrineofspontaneousgenerationinthesecondhalfof

the 19 thcenturythatanewwayofthinkingbecamepossible.Bytheendof

thatcentury,microorganismshadbeenidentifiedasthecausalagentsin

manyfamiliardiseasesbyapplyingtheHenle-Kochpostulatesformulated

byR.Kochin 1 890.

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Kayser, Medical Microbiology © 2005 Thieme