Types of bacterial adhesions
Mostly proteins, sometimes glycoconjugates or lipoteichnoic acid.
Nonfimbiral adhesin.
P fimbirae.
Type IV pili.
Curli.
Characteristics of adhesins
Adheison to host clel surfaces or EZM.
Determines tissue tropism.
Consequences: Colonization, penetration, triggering of host reposnse, uptake into host cell
non-fimbrial adhesins
Anchored in bacterial membrane.
Deirect binding to host cell molecule or via bridging.
Gram-pos/neg.
P pili (E.coli)
P: pyelonephritis-ass. Pap operon. Type II secretion system. Bind glycolipids. Host cells: upper urinary tract.
Number of adhesins
Bacteria often contain multiple. Often act synergistically. Can be functionally redundent > rarely essential VF
Possible adhesin targets
Cadherings
Ig
Selectins
beta1-integrins
EPEC/EHEC adherence
Initial binding via type IV pilus. Second adhesin: intimin (adheres to TIR which is translocated via type III secretion system)
RGD site
Eukaryotic binding site for integrins.
Arg-Gly-Asp tripeptice.
Some bacterial adhesins mimic RGD site.
Example for molecular mimicry
Filmanetous hemagglutinin FHA of Bordetella perfussis.
Nonfimbiral adhesin.
FHA binding activities
- Carbohydrate binding to ciliated cells of resp. tract
- heparan sulfate binding to EZM on epithelial cells
- integrin binding via RGD site on phagocytes
(>molecular mimicry!)
Bordetellla pertussis
Replicates on ciliated cells of nasopharyngeal/upper resp. tract.
Whooping cough.
Binds to epithelial cells/monocytes in resp. tract.
Vaccine available.
Mycobacterium leprae - tropism?
Obligatory intracellular (T!). Tropism for Schwann cells: PGL1 binds laminin (laminin receptors on Schwann cells: alpha-dystroglcan and beta4-integrins)
Adherence of staphylococci and streptococci
Via host bridging molecule.
Common host molecules: ECM components (eg collagen)
Species-specifity (eg S.aureis > fibrin)
Phase variation
Regulated expression of adhesins in response to environmental signals > sequential binding to diff host cell structures.
Immune evasion.
Example for phase variation
Neisseria.
Isoforms of Opa (and Opc) protein > interaction with different cells.
> Opa-HS, Opa-CEA, Opc
> > immune evasion
Yersinia - penetration
Invasin: nonfimbrial adhesins, bind beta1-integrins.
Zipper-like uptake: phagocytosis by M cells
Listeria - penetration
Express interlin A > binds E-cadhering > zipper-like uptake by epithelial cells
Plasmodium falciparum - adhesion
Adhesin: PfEMP1
Exported though host cell (erys) > forms knobs > erys adhere to endothelial cells of large (immunevasion) or small blood vessels (occlusion > inflammation)
antigenic variation in PfEMP1
Encoded by various genes, only one expressed at a time > can switch > prolonged infections
> > immune evasion
Function of UPEC adhesins
P/Type I pili
> pathogen is not washed out
General types of binding partners of bacterial adhesins
Cell-surface receptors
ECM proteins
bridging molecules
