Medical Microbiology

292 4 BacteriaasHumanPathogens

Escherichiacoli....................................................

&ThenaturalhabitatofE.coliistheintestinaltractofhumansandanimals.

Itisthereforeconsideredanindicatororganismforfecalcontaminationof

waterandfoods.E.coliisthemostfrequentcausativepathogeninhuman

bacterialinfections.Extraintestinalinfectionsincludeurinarytractinfec-

tions,whichoccurwhenthetractisobstructedorspontaneouslycaused

bythepathovarUPEC.Themostimportantothercoliinfectionsarecholecys-

titis,appendicitis,peritonitis,postoperativewoundinfections,andsepsis.

IntestinalinfectionsarecausedbythepathovarsEPEC,ETEC,EIEC,EHEC,

andEAggEC.EPECandEAggECfrequentlycausediarrheaininfants.ETEC

produceenterotoxinsthatcauseacholeralikeclinicalpicture.EIECcausea

dysenterylikeinfectionofthelargeintestine.EHECproduceverocytotoxins

andcauseahemorrhagiccolitisaswellastherarehemolytic-uremicsyn-

drome.E.colibacteriainfectionsarediagnosedbymeansofpathogeniden-

tification. &

Generalcharacteristics.ThenaturalhabitatofE.coliistheintestinesofani-

malsandhumans.Thisbacteriumisthereforeusedasanindicatorforfecal

contaminationofdrinkingwater,bathingwater,andfoods.Guidelineregula-

tions: 100 mlofdrinkingwatermustnotcontainanyE.coli.Surfacewater

approvedforbathingshouldnotcontainmorethan 100 (guidelinevalue)

to 2000 (absolutecutoffvalue)E.colibacteriaper 100 ml.

E.coliisalsoanimportanthumanpathogen.Itisthebacterialspeciesmost

frequentlyisolatedfrompathologicalmaterials.

Morphology,culture,andantigenstructure.TheGram-negative,straight

rodsareperitrichouslyflagellated.Lactoseisbrokendownrapidly.Thecom-

plexantigenstructureofthesebacteriaisbasedonO,K,andHantigens.Fim-

brialantigenshavealsobeendescribed.Specificnumbershavebeenassigned

totheantigens,e.g.,serovarO18:K1:H7.

Pathogenesisandclinicalpictureofextraintestinalinfections.Extraintes-

tinalinfectionsresultfromrelocationofE.colibacteriafromone’sownflora

toplacesonorinthemacroorganismwheretheyarenotsupposedtobebut

whereconditionsfortheirproliferationarefavorable.

&Urinarytractinfection.Suchaninfectionmanifestseithersolelyinthe

lowerurinarytract(urethritis,cystitis,urethrocystitis)oraffectstherenal

pelvisandkidneys(cystopyelitis,pyelonephritis).Inacuteurinarytractin-

fections,E.coliisthecausativeorganismin 70 – 80 %ofcasesandinchronic,

persistentinfectionsin 40 – 50 %ofcases.

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Kayser, Medical Microbiology © 2005 Thieme