Kachur - Topic 3 - Adhesion and Invasion

Question 1

How do extracellular bacteria adhere to host cells

Answer 1

adherence allows bacteria to resist the mechanical clearing mechanism of the host

Question 2

What are adhesions?

Answer 2

bacterial components that mediate interaction between the bacterium and the host cell surface

Question 3

How do adhesins bind specifically to host cells

Answer 3

• host cells have molecules on surface co-opted by pathogens
• ## high degree of specificity b/w adhesion + host recognition site

Question 4

What is a example of a receptor used for bacterial adhesins?

Answer 4

host surface glycans

Question 5

What are the three types of pili?

Answer 5

• type I, F1 and type IV

Question 6

What is the function of pili?

Answer 6

used for attachment to surfaces, other cells or bacteria

Question 7

Where are pili found?

Answer 7

in both gram negative and gram positive bacteria

Question 8

What are some pili characteristics

Answer 8

• fragile and constantly replaced therefore lots of opportunity
• pili can transition from swimming to surface-associated state that requires genetic changes to new surface state
• highly antigenic but heavily glycosylated to hide antigenic site
• allow velcro-like attachment to surfaces

Question 9

What are type I pili?

Answer 9

rigid, long, and thin fragments that protrude off Gram negative bacteria

Question 10

What is the unique feature of type I fili?

Answer 10

is that they induce hemagglutination (RBC aggregates)

Question 11

What are type I pili made of?

Answer 11

composed of polymerized subunits of pilin protein
- length of pilus can range from 0.5uM to 10 uM

Question 12

What is the chaperone/usher pathway?

Answer 12

assembles proteinaceous filaments on bacterial surfaces
- pili components are secreted by sec-transport pathway + chaperone usher pathway
these operons encode at least three minimum different proteins: chaperone, usher, and pilin

Question 13

What is F1 pili?

Answer 13

shorter, linear, and flexible polymers that have a tendency to aggregate

Question 14

Where is the F1 capsular antigen expressed?

Answer 14

expressed exclusively on Yersinia pestis

Question 15

What are characteristics of F1 pili?

Answer 15

• antiphagocytic: prevents uptake by macrophages
• similar to type I/P pilus in that it uses CU system

Question 16

What does the F1 capsule consist of?

Answer 16

tangle of thin, linear Caf1 fibers
- lots of variability (limited vaccine development)
- pilus is expressed @ 31 degrees but not 21 degrees

Question 17

What are the different types of bacteria with type IV pili?

Answer 17

• EPEC
• Neisseria gonorrhoeae
• Neisseria meningtidis

Question 18

How does binding of EPEC work?

Answer 18

• binding mode of bundling recognized LacNAc (N-acetylelactosamine) groups on host cells
• binding causes upregulation of virulence genes in bacterium and retraction of the pilus

Question 19

What are characteristics of type IV pili?

Answer 19

• can retract while the pilus tip remains firmly adhered to the target surface leading to twitching motility
• in some bacteria, pilin is glycosylated
• in some bacterial species, such as EPEC and V. cholerae, type IV pili can aggregate laterally forming bundles

Question 20

Pathogen profile: porphyromonas gingivalis (gram negative)

Answer 20

• microbial dybiosis on the teeth is facilitated by a shift in the microbiome towards Gram negative anaerobes
• keystone pathogen by production of a virulence factor called gingipain (cysteine protease)
• cleaves complement C5 protein into C5a which activates the C5a receptor and increases the inflammatory response but at the same time prevents microbial killing by leukocytes
• interesting - P. gingivalis does not need to be present i high number to initiate a disease state

Question 21

What is twitching motility?

Answer 21

surface motility powered by the extension and retraction of type IV pili, which confers slow cell movement, often with a jerky or twitchy appearance
- motility seems to be required for virulence and may help engage the Type II secretion systems for the injection of toxins

Question 22

What pili can bind DNA

Answer 22

type IV

Question 23

Pathogen profile: Neisseria meningitides

Answer 23

• gram (-)ve bacterium; aka meningococcus
• exclusively human pathogen
• can cause meningitis and other forms of meningococcal disease
• about 10% of adults are carriers of the bacteria in their nasopharynx
• main cause of bacterial meningitis in children and young adults
• causes developmental impairment and death in about 10% of cases

Question 24

How does DNA binding work in Neisseria meningitidis?

Answer 24

DNA transformation requires the presence of short DNA uptake sequences residing in coding regions of the donor DNA
DNA transferred often contains virulence genes including toxin resistance and antibiotic resistance
- fimbrae facilitate uptake of DNA = spreads virulence and causes resistance

Question 25

How does meningoccocal type IV pili bind DNA

Answer 25

minor pilin ComP
- involved in natural competence that allows transformation

Question 26

How does ComP work in Neisseria species?

Answer 26

• highly conserved
• only DNA sequence with homology (sequence similarity)
• will be integrated into genome

Question 27

What are biofilms

Answer 27

dense, multiorganismal layers of bacterial communities attached to surfaces
- attachment to surfaces is mediated by an EPS - extracellular polysaccharide slime
- primary colonizers of biolfilms include Clostridia spp and Pseudomonas aeruginosa

Question 28

Pathogen profile: Pseudomonas aeruginosa

Answer 28

• example of opportunistic pathogen
• primarily a nosocomial pathogen
• rod shaped, gram (-)ve, aerobic bacteria
• cause:
  UTI, respiratory infections, GI infections

Question 29

Why is pseudomonas aeruginosa such a opportunistic pathogen

Answer 29

natural habitat
- ubiquitous in soil + water
metabolism
- metabolically diverse: anerobic, aerobic
- can grow on 75 different organic substrates
nutritional requirements
- minimal nutritional needs: might not be reproducing; tolerant to more conditions
optimal growth temperature
- wide temperature range of 0-37 degrees
tolerance to physical conditions
- often grows in biofilms
- resistance to detergents + high salt
resistant to antibiotics + phagocytes
- antibiotic resistant genes have evolved
- associate with biofilms

Question 30

What is the sortase enzyme

Answer 30

• catalyzes transpeptidation step of pilin synthesis
• important virulence factor or gram positive pathogens
• sortase enzymes are a group of prokaryotic enzymes that promote the covalent anchoring of surface proteins to the cell wall envelope to enable each microbe to effectively interact with its environment

Question 31

What are the main functions of the sortase enzyme?

Answer 31

• cleave surface proteins + allow rearrangments + modifications
  1) sorts protein of the cell surface + covalently links to cell wall
  2) polymerizes pilin proteins: makes a sticky chain of adherance proteins