Medical Microbiology

Host–PathogenInteractions 17

&Secretionofvirulenceproteins.Proteinsaresynthesizedattheribo-

somesinthebacterialcytoplasm.Theymustthenbesecretedthroughthe

cytoplasmicmembrane,andinGram-negativebacteriathroughtheouter

membraneaswell.Thesecretionprocessisimplementedbycomplexprotein

secretionsystems(I-IV)withdifferingcompositionsandfunctionalpath-

ways.ThetypeIII(virulence-related)secretionsystemincertainGram-neg-

ativebacteria(Salmonella,Shigella,Yersinia,Bordetella,Escherichiacoli,Chla-

mydia)isparticularlyimportantinthisconnection(seeFig. 1. 3 ).

Table 1. 5 Continued:ExamplesofBacterialToxins

Toxin Cell

specificity

Moleculareffect Contributionto

clinicalpicture

Superantigentoxins

Toxicshocksyn-

drometoxin-1

(TSST-1)

(Staphylococcus

aureus)

Tlympho-

cytes;ma-

crophages

Stimulationofsecretion

ofcytokinesinTcellsand

macrophages.

Fever;exanthem;

hypotension.

NeedleComplexofTypeIIISecretionSystem

Outer

membrane

Inner

membrane

Periplasmic space

Fig. 1. 3 When certain Gram-nega-

tiverodbacteriamakecontactwith

eukaryotictargetcells,asensormole-

culeinteractswithareceptoronthe

targetcells.Thisinteractionresults

intheopeningofasecretionchannel

oftheso-called“needlecomplex”(ex-

tendingthroughboththecytoplasmic

membraneandoutermembrane)and

informationofaporeinthemem-

braneofthe targetcell.Through

theporeandchannel,cytotoxicmole-

culesarethentranslocatedintothe

cytosol of the target cell where

they,forexample,inhibitphagocyto-

sisandcytokineproduction(inmacro-

phages),destroythecytoskeletonof

thetargetcell,andgenerallywork

toinduceapoptosis.

1

Kayser, Medical Microbiology © 2005 Thieme