Medical Microbiology

Escherichiacoli 293

Urinarytractinfectionsresultfromascensionofthepathogenfromthe

ostiumurethrae.Developmentofsuchaninfectionisalsofurtheredbyob-

structiveanomalies,aneurogenicbladderoravesicoureteralreflux.Urinary

tractinfectionsthatoccurintheabsenceofanyphysicalanomaliesareoften

causedbythepathovarUPEC(uropathogenicE.coli).UPECstrainscanattach

specificallytoreceptorsoftherenalpelvismucosawithpyelonephritis-asso-

ciatedpili(PAP,Pfimbriae,p. 1 58)ornonfimbrialadhesins(NFA).Theypro-

ducethehemolysinHlyA.

&Sepsis.E.colicausesabout 15 %ofallcasesofnosocomialsepsis(S.aureus

20 %).AnE.colisepsisisfrequentlycausedbythepathovarSEPEC,which

showsserumresistance(p. 1 3).

&OtherE.coliinfections.Woundinfections,infectionsofthegallbladder

andbileducts,appendicitis,peritonitis,meningitisinprematureinfants,neo-

nates,andveryelderlypatients.

Pathogenesisandclinicalpicturesofintestinalinfections.E.colithatcause

intestinalinfectionsarenowclassifiedinfivepathovarswithdifferingpatho-

genicityandclinicalpictures:

&EnteropathogenicE.coli(EPEC).Thesebacteriacauseepidemicorspora-

dicinfantdiarrheas,nowrareinindustrializedcountriesbutstillamaincon-

tributortoinfantmortalityindevelopingcountries.EPECattachthemselves

totheepithelialcellsofthesmallintestinebymeansoftheEPECadhesion

factor(EAF),theninjecttoxicmoleculesintotheenterocytesbymeansofa

typeIIIsecretionsystem(seep. 1 7).

&EnterotoxicE.coli(ETEC).Thepathogenicityofthesebacteriaisduetothe

heat-labileenterotoxinLT(inactivationat 608 Cfor 30 minutes)andtheheat-

stabletoxinsSTaandSTb(cantoleratetemperaturesupto 1008 C).Some

strainsproduceallofthesetoxins,someonlyone.LTisverysimilartocholera

toxin.Itstimulatestheactivityofadenylatecyclase(seep. 29 8).STastimulates

theactivityofguanylatecyclase.(cGMPmediatestheinhibitionofNa+absorp-

tionandstimulatesCl–secretionbyenterocytes.)ETECpathogenicityalsode-

rivesfromspecificfimbriae,so-calledcolonizingfactors(CFA)thatallowthese

bacteriatoattachthemselvestosmallintestineepithelialcells,thusprevent-

ingtheirrapidremovalbyintestinalperistalsis.TheenterotoxinsandCFAare

determinedbyplasmidgenes.TheclinicalpictureofanETECinfectionischar-

acterizedbymassivewaterydiarrhea.Thediseasecanoccuratanyage.Once

theillnesshasabated,alocalimmunityisconferredlastingseveralmonths.

&EnteroinvasiveE.coli(EIEC).Thesebacteriacanpenetrateintothecolon-

icmucosa,wheretheycauseulcerous,inflammatorylesions.Thepathogen-

esisandclinicalpictureofEIECinfectionsarethesameasinbacterialdys-

entery(p.288).EIECstrainsareoftenlac-negative.

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Kayser, Medical Microbiology © 2005 Thieme