Medical Microbiology

Host–PathogenInteractions 11

Therearefivegroupsofpotentialbacterialcontributorstothepathogen-

esisofinfectiousdiseases:

1. Adhesins.Theyfacilitateadhesiontospecifictargetcells.

2. Invasins.Theyareresponsibleforactiveinvasionofthecellsofthemacro-
   organism.


3. Impedins.Thesecomponentsdisablehostimmunedefensesinsome
   cases.


4. Aggressins.Thesesubstancesincludetoxinsandtissue-damagingen-
   zymes.


5. Modulins.Substancesthatinduceexcesscytokineproduction(i.e.,lipo-
   polysaccharidesofGram-negativebacteria,superantigens,mureinfrag-
   ments).

Adhesion................................................

Whenpathogenicbacteriacomeintocontactwithintacthumansurfacetis-

sues(e.g.,mucosa),theycontrivetoadheretoreceptorsonthesurfaceofthe

targetcellsbymeansofvarioussurfacestructuresoftheirown(attachment

Virulence,Pathogenicity,Susceptibility,Disposition

virulent

avirulent

pathogenic

susceptible

disposed

resistant

strain

species

variety

individual

apathogenic

nonsusceptible

type or var

(e.g., serotype, serovar)

Fig. 1. 1 Pathogenicityreferstopathogens,susceptibilitytohostspecies.The

termvirulencereferstoindividualstrainsofapathogenspecies.Thetermsdisposi-

tionandresistanceareusedtocharacterizethestatusofindividualsofasuscep-

tiblehostspecies.

1

Kayser, Medical Microbiology © 2005 Thieme