Medical Microbiology

16 1 GeneralAspectsofMedicalMicrobiology

Table 1. 5 ExamplesofBacterialToxins;MechanismsofActionandContribu-

tiontoClinicalPicture

Toxin Cell

specificity

Moleculareffect Contributionto

clinicalpicture

ABtoxins

Diphtheriatoxin

(Corynebacterium

diphtheriae)

Manydif-

ferentcell

types

ADP-ribosyltransferase.

Inactivationofribosomal

elongationfactoreEF2

resultingfromADP-ribosy-

lationduringproteinsyn-

thesis;leadstocelldeath.

Deathofmucosal

cells.Damageto

heartmusculature,

kidneys,adrenal

glands,liver,motor

nervesofthehead.

Choleratoxin

(Vibriocholerae)

Enterocytes ADP-ribosyltransferase.

ADP-ribosylationofregula-

toryproteinGsofadenylate

cyclase,resultinginper-

manentactivationofthis

enzymeandincreasedlevels

ofcAMP(secondmessenger)

(seeFig.4. 20 ,p.298).Result:

increasedsecretionofelectro-

lytes.

Massivewatery

diarrhea;severe

lossofelectrolytes

andwater.

Tetanustoxin

(Clostridium

tetani)

Neurons

(synapses)

Metalloprotease.Proteolytic

cleavageofproteincompo-

nentsfromtheneuroexo-

cytosisapparatusinthesyn-

apsesoftheanteriorhorn

thatnormallytransmitinhibit-

ingimpulsestothemotor

nerveterminal.

Increasedmuscle

tone;crampsin

striatedmuscula-

ture.

Membranetoxins

Alphatoxin

(Clostridium

perfringens)

Manydif-

ferentcell

types

Phospholipase. Cytolysis,resulting

tissuedamage.

Lysteriolysin

(Listeriamono-

cytogenes)

Manydif-

ferentcell

types

Poreformationinmem-

branes.

Destructionofpha-

gosomemem-

brane;intracellular

releaseofphagocy-

tosedlisteriae.

1

Kayser, Medical Microbiology © 2005 Thieme