6) Adhesion

• one of the body’s innate immune defenses is the ability to physically remove bacteria from the body

• done via shedding of surface epithelial cells

  • by coughing, sneezing, vomiting and diarrhea

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

• —> successfull infection by bacterial pathogens requires adhesion to host cells —> specific ligand-receptor interaction

• adhesins

• capsules

• flagella

• other cell wall-associated molecules

Pili:

• pili are thin protein tubes and are found in virtually all Gram-negative bacteria (not many Gram-positive)

• pili have a shaft composed of the protein pilin

• shaft end has an adhesive tip structure -> shape corresponds to specific receptors on host cells

• pili enable some organisms to adhere to receptors on host cells (and thus resist flushing by the body)

Processes

• once attached to the host cell -> pili can depolymerize and enable adhesions in the bacterial cell wall to make more intimate contact

• binding of pili to host cell receptors can trigger synthesis of additional cell wall adhesins

• bacteria are constantly losing and reforming pili -> switch types of adhesives tips in order adhere to different cell types and evade immune system

• neisseria gonorrhoeae

• escherichia coli

• salmonella

• vibrio cholerae

• pseudomonas aeruginosa

• UPEC -> Uropathogenic E. coli

• 2 important type of pili:

  • Type 1 pili, encoded by the fim operon —> expresses a hemagglutinin which recognizes mannose (present on bladder epithelium)

  • Pap-pili encoded by the pap operon —> interacts with the di-galactoside unit in the P-blood group antigen (??)

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• type IV pili allows attachment to cells, food and fibers and enables twitching / gliding motility (located at the poles of the cell)

• extension and retrection of these pili allows the bacterium to drag itself along the solid surface

• other functions include biofilm formation and molecule exchange

adhesins are surface proteins found in the cell wall of various bacteria that bind to specific receptor molecules on the surface of host cells

MSCRAMMS - microbial surface components recognising adhesive matrix proteins

MSCRAMMs share a similar structure -> two adjacent IgG-like folded subdomains mediating their attachment to components of the host

• dock lock latch

• collagen hug

• tandem β-zipper

• capsules are polysaccharide layers that surround some bacteria

• they help in adhesion by being sticky, allowing bacteria to cling to surfaces

• biofilm formation starts with adhesion; capsules facilitate initial attachment

usually used for motility but also reported to be used as an adhesive organelle

• E. coli

• Pseudomonas aeruginosa

• Closteridioides difficile

• Hallmark of EPEC infection is formation of attaching and effacing (A/E) lesions in the intestinal epithelium

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

• LEE encodes

  • the adhesin intimin

  • T3SS (Type 3 secretion system) —> inject effector proteins into intestinal epithelial cells —> cause polymerization of actin at the cell surface -> pushes host cell cytoplasmic membrane to form a pedestral

• H. pylori use a type 4 secretion system to inject effector proteins into stomach epithelial cells

• induces host cells to display more receptors on their surface for H. pylori adhesins (CagA)

• uses filamentous hemagglutinin —> allows bacterium to adhere to galactose residues of glycolipids

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

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

• Opa enables bacterium to make 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

• Borellia burgdoferi

• Treponema pallidum (also spirochete)

• Streptococcus pyogenes