6 Adhesion

• Removal of bacteria by such means as coughing, sneezing, vomiting, and diarrhea

• Bacterial removal by bodily fluids such as saliva, blood, mucous, and urine

Adhesins are binding proteins, usually on tips of long fibrillary organelles called fimbriae or pili, that are anchored to the cell wall

Adhesins are critical to biofilm formation

• Biofilms are multicellular communities that are 1000-fold more resistant to antibiotics and immune defense than are planktonic (swimming or drifting) bacteria

Pili enable some organisms to adhere to receptors on target host cells and thus colonize and resist flushing by the body

• Pilus has a shaft composed of the protein pilin

• Shaft end has an adhesive tip structure

• shape corresponds to specific glycoprotein or glycolipid receptors on host cells

• Once attached to host cells, pili can depolymerize and enable adhesions in the bacterial cell wall to make more intimate contact

• Also evidence that binding of pili to host cell receptors can serve as a trigger for activating the synthesis of additional cell wall adhesins

Escherichia coli & Salmonella

Yes, in order to adhere to different cell types and evade immune defenses

e.g., E. coli is able to make over 30 different types of pili

Both types of pili are heteropolymeric

→ Major pilus protein subunit provides pilus stalk

→ Several minor subunit proteins at distal end

→ PapG and FimH represent the actual adhesins

→ Chaperone-usher (CU) pathway assembles pili

• P pilus is composed of 6 different subunits arranged into two distinct subassemblies (tip fibrillum and pilus rod)

• At distal end, tip fibrillum is composed of 1x PapG adhesin followed by PapF and PapE subunits

• Pilus rod is made by >1,000 copies of PapA subunit

• Adaptor subunit PapK connects above subunits to the PapA rod (superhelical structure at base of the pilum)

• attachment to cells, food and fibers and enables twitching motility

• Located at poles of cell and allows for a gliding motility along a solid surface such as a host cell

• Extension and retraction of these pili allows the bacterium to drag itself along the solid surface

• Other functions include biofilm formation and molecule exchange (e.g. DNA)

• These pili are strong, flexible rod -like filaments of 5 –8 nm in diameter and 1 –2 μm in length -

• Pilin subunits are assembled through interactions between their conserved N - terminal α-helices

  → forms a hydrophobic core in the filament that is believed to provide extreme mechanical strength

• Type IV pili bind to the glycolipids asialo - GM1 and asialo-GM2 on epithelial cell surfaces -

• In Pseudomonas and Neisseria, type IV pili are believed to be a major virulence- associated adhesin

Adhesins are surface proteins found in the cell wall of various bacteria that bind to specific receptor molecules on the surface of host cells → enable bacterium to adhere intimately to that cell in order to colonize and resist physical removal

microbial surface components recognising adhesive matrix proteins

• bind host proteins

• may aid adherence to host tissues, and serum-coated plastic

• provides a critical step to establish infection

• important in Gram+ve’s

• ‘dock lock latch ’

• ‘collagen hug’

• tandem β-zipper

Many bacteria produce a capsular polysaccharide matrix or glycocalyx

movement and chemotaxis

Some of these effector proteins cause polymerization of actin at the cell surface

→ pushes host cell cytoplasmic membrane up to form a pedestal

Another effector protein inserts into the membrane of the pedestal to serve as a receptor molecule for E. coli adhesins

attaching and effacing (A/E) lesions in the intestinal epithelium

Hallmark of EPEC (Pathogenic E. coli) infection

Formation of A/E lesions is mediated by genes located on the pathogenicity island locus of enterocyte effacement (LEE)

• encodes the adhesin intimin

• T3SS • six effectors

  • including essential translocated intimin receptor (Tir)

• → interaction between Tir and intimin anchors the bacterium to host membrane

H. pylori use a type 4 secretion system (T4SS) to inject effector proteins into stomach epithelial cells → induces host cells to display more receptors on their surface for H. pylori adhesins

• CagA

H. pylori causes chronic gastritis, peptic ulcers, and gastric cancer in humans

Filamentous hemagglutinin is an adhesin that allows the bacterium to adhere to galactose residues of glycolipids on respiratory tract ciliated epithelial cells

• Pertussis toxin also functions as an adhesion

  • One subunit of pertussis toxin remains bound to the bacterial cell wall while another subunit binds to glycolipids on membrane of ciliated epithelial cells of respiratory tract

• Pertussis also produces an adhesin called pertactin that further enables the bacterium to adhere to cells

• B. pertussis causes whooping cough

Neisseria gonorrhoeae produces an adhesin called Opa (protein II) that enables the bacterium to make a more intimate contact with host cell after it first adheres with its pili

Like with adhesive tips of pili, N. gonorrhoeae has multiple alleles for Opa protein adhesins enabling the bacterium to adhere to a variety of host cell types

N. gonorrhoeae is a bacterial pathogen responsible for gonorrhoea