Medical Microbiology

282 4 BacteriaasHumanPathogens

Pathogenicitydeterminants.Anumberoffactorsareknowntoplayarolein

thepathogenicityofvariousEnterobacteriaceaeinfections.Themostimpor-

tantare:

&Adhesionfactors.Attachmentfimbriae,attachmentpili,colonizingfactor

antigens(CFAs).

&Invasivefactors.Proteinslocalizedintheoutermembrane(invasins)that

facilitatetheinvasionoftargetcells.

&Exotoxins.

— Enterotoxinsdisturbthenormalfunctioningofenterocytes.Stimulationof

adenylateorguanylatecyclase;increasedproductionofcAMP(seep. 29 8).

Thisresultsinthelossoflargeamountsofelectrolytesandwater.

— Cytotoxinsexertadirecttoxiceffectoncells(enterocytes,endothelial

cells).

&Endotoxin.ToxiceffectoflipoidAasacomponentofLPS(p. 1 56).

&Serumresistance.ResistancetothemembraneattackcomplexC5b6789

ofthecomplementsystem(p.86ff.).

&Phagocyteresistance.Makessurvivalinphagocytespossible.Resistance

againstdefensinsand/oroxygenradicals(p.23).

&CumulationofFe2+.ActivetransportofFe2+bysiderophoresinthebac-

terialcell(p. 1 3).

Salmonella(Gastroenteritis,TyphoidFever,ParatyphoidFever)...

&AllsalmonellaeareclassifiedinthespeciesSalmonellaentericawith

sevensubspecies.Nearlyallhumanpathogensalmonellaearegroupedunder

S.enterica,subsp.enterica.Salmonellaearefurthersubclassifiedinover 2000

serovarsbasedontheirOandHantigens,whichusedtobe(incorrectly)

designatedasspecies.

TyphoidsalmonellosesarecausedbytheserovarstyphiandparatyphiA,B,

andC.Thesalmonellaearetakenuporallyandtheinvasionpathwayis

throughtheintestinaltract,fromwheretheyenterlymphatictissue,first

spreadinglymphogenously,thenhematogenously.Ageneralizedsepticclin-

icalpictureresults.Humancarriersaretheonlysourceofinfection.Transmis-

sioniseitherdirectbysmearinfectionorindirectviafoodanddrinkingwater.

Anti-infectiveagentsarerequiredfortherapy(ampicillin,cotrimoxazole,

4-quinolones).Anactivevaccineisavailabletoprotectagainsttyphoidfever.

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Kayser, Medical Microbiology © 2005 Thieme