Adhesins

Question 1

Give an example of a pathogen confined to epithelium

Answer 1

Vibrio cholerae
•colonise intestinal tract
•causes cholera

Bordetella pertussis
•colonises the respiratory tract
•causes whooping cough

Question 2

Give an example of a pathogen that invades into deeper tissue to cause a systemic infection

Answer 2

Salmonella enterica serovar Typhi
•colonises intestinal tract
•causes typhoid fever (systemic)

Legionella pneumophila
•colonises respiratory tract
•causes legionellosis (systemic)

Question 3

How does mucous inhibit bacterial colonisation?

Answer 3

•mucous contains mucins
•mucins are filamentous proteins, ~80% glycosylated
•glycosyl chains protect peptide from degradation and are receptors for bacterial surface ligands
•mucins bind to and trap bacteria

Question 4

What is mucous secreted by?

Answer 4

Goblet cells and subepithelial glands

Question 5

Some examples of mechanical removal of bacterium by host

Answer 5

•eyes: blinking, tearing
•oral cavity: salivary flow, chewing
•RT: mucociliary escalator, sneezing, coughing, swallowing
•GIT: peristalsis, excretion
•UT: urination

Question 6

What are the steps to colonisation

Answer 6

1. Avoid being trapped in mucous
2. Penetrate mucous -> reach the epithelium
3. Adhesion via adhesins

Question 7

What are methods of penetrating the mucous to reach epithelium?

Answer 7

Motility (flagella)
•vibrio cholera
•helicobacter pylori

Mucinases
•vibrio cholera
•shigella flexneri

Question 8

Epithelial cell receptors

Answer 8

•glycoproteins and glycolipids
•adhesins bind to sugar moiety

Question 9

Fimbrial/pilus adhesins

Answer 9

•bacteria and epithelial cell are both negatively charged (electrostatic repulsion)
•pilus extends past the bacterial capsule layer
•the extended pilus overcomes electrostatic repulsion
•binds to host glycoproteins or glycolipids

Question 10

Afimbrial adhesins

Answer 10

•adhesins bind to host cell surface protein or carbohydrate
•exopolysaccharide (EPS) capsule covers afimbrial adhesins

Question 11

Composition and structure of pili

Answer 11

Shaft
•repeating subunits (pilins)
•assembled in helical array

Tip
1- specialised tip has adhesive subunits at the end of the pilus
2- can have no tip protein and no specialised structure
3- can have adhesive subunits along the shaft

Question 12

Describe the structure of the Pap pili

Answer 12

•shaft is ~1000 subunits of PapA

Fibril
•1 PapK monomer
•5-10 PapE subunits
•1 PapF monomer

•1 PapG monomer at the very tip

Question 13

What pathogen has the Pap pili?

Answer 13

•pyelonephritis associated pili
•uropathogenic E. coli (UPEC)
•causes UTIs, bladder, kidney infection

Question 14

What the fuck is fibrillae

Answer 14

•resemble pili, different structure
•finer than pili, kind of like a fuzz around a cell as opposed to ‘hair’ from pili
•long multidomain proteins attached at surface
•have an adhesive domain at the tip
•multiple tandemly repeated domains make stalk

Question 15

Give an example of a fibrillae

Answer 15

•M protein in Streptococcus
•role in adhesion

Question 16

Explain the receptor for Pap pili

Answer 16

•Pap pili found on UPEC (cause UTIs)
•adhesin is PapG at pilus tip
•receptor is globotriasylceramide (glycosphingolipid)
•gal-alpha1,4-gal of receptor binds pilus tip
•uroepithelial cells have this receptor

Question 17

What’s another pilus used by UPEC?

Answer 17

•type 1 pili
•has FimH protein at pilus tip
•receptor is mannose-containing glycoproteins

Question 18

Give an example of a bacteria that uses afimbrial adhesins

Answer 18

•OMPs of gram negatives contribute to tighter binding after anchoring via pilus
•Neisseria meningitidis

Question 19

What are the advantages of anti-virulence agents?

Answer 19

Avoids resistance development
•agents don’t kill the bacteria, so developing resistance would not provide a survival advantage

•potentially species or strain specific
•would not have an impact on microbiota

Question 20

What are some potential anti-virulence strategies?

Answer 20

•anti-adhesion agents
•anti-quorum sensing
•anti-biofilm
•antitoxin
•anti-T3SS

Question 21

Explain the vaccine potential of adhesins

Answer 21

•purified pili proteins
•antibodies against pili proteins
•antibodies block adhesin binding pocket- inhibits pathogen binding
•antibodies can opsonise the pathogen -> phagocytosis

Question 22

Give examples of potential adhesin vaccines

Answer 22

•K88 pili (ETEC)- vaccination of pigs
•K99 pili (ETEC)- vaccination of cows, pigs, sheep

Question 23

What are anti-adhesin drugs

Answer 23

Stable, high affinity analogues of receptors
•competitively inhibit binding of adhesins
•prevent colonisation and therefore infection

Or inhibitors of pilus assembly (pilicides)

Question 24

UPEC example of receptor anti-adhesins

Answer 24

•high affinity analogue of gal-alpha1,4-gal will bind to Pap pili (PapG)

•hydrophobic a-mannoside compounds bind type 1 pili (FimH)

Question 25

Example of pilicide

Answer 25

•Pap and type 1 pilus subunits form helical array •assembly is via pilin chaperones (periplasmic proteins) •chaperones interact with C-terminal residues of pilin subunits •PapD is chaperone •pilin subunits are added starting with PapG, then F, then E •2-pyridones resemble PapG C-terminus and inhibit chaperone binding

Question 26

Problems and challenges of anti-adhesins

Answer 26

'cocktail' mixtures may be necessary •multiple adhesins on 1 pathogen are common (ETEC) •multiple adhesins are expressed in a time and tissue specific manner Rapid and precise diagnosis is needed Drug may be non-specific and interfere with microbiome Drug may be weak in vivo

Question 27

How do beneficial bacteria help prevent colonisation?

Answer 27

Indirectly •microbiota stimulated host immunity Directly •mediated by normal flora, antagonise with pathogen •directly compete for same niche •secrete antimicrobial peptides and toxins

Question 28

What are bacteriocins?

Answer 28

•small, antibacterial proteins secreted by flora

Question 29

What's an example of a bacteriocin?

Answer 29

•bacteriocin secreted by oral Streptococcus mutans •inhibits other streptococci (S. pyogenes)