WEEK 1 - bacteria adhesion (Human health+disease)

Question 1

attachment

Answer 1

specific interaction between bacterium and host

Question 2

attachment
- on the bacterium

Answer 2

adhesion such as fimbriae/pili, surface proteins

Question 3

attachment
- on the host cell

Answer 3

receptors such as host membrane glycoproteins, glycolipids, mucus

Question 4

attachment
- colonisation

Answer 4

attachment to surfaces

Question 5

invasion

Answer 5

entry to host cells

Question 6

structure of gram positive pili

Answer 6

major pilin subunits are covalently linked
- long and stick out from surface

minor ancillary proteins are adhesins

pilus is anchored to the peptidoglycan (covalently)

Question 7

pili are important in:

Answer 7

bacterial adhesion, colonization, biofilm formation, translocation across host membranes and invasion of host tissues

Question 8

pilus assembly

Answer 8

subunits secreted through Sec

sortase enzyme recognises LPXTG motif

forms a covalent link tp:
a) pilin subunit
b) peptidoglycan

Question 9

streptococcus pneumoniae

Answer 9

gram positive

main cause of community acquired pneumonia

also causes meningitis, bacteraemia, and infection of middle ear

readily colonise mucosal surfaces

Question 10

adhesion of streptococci to cell surfaces

Answer 10

1. pili interact with host cell or extracellular matrix
   - Net negative charge –> need to break across repulsion to adhere –> long filaments are helpful to overcome this
2. zippering effect - bacteria brought closer to host (so can get more interaction)
3. other adhesins on bacterial surface result in very close adhesion
4. pilus - mediated bacterial aggregation
   - microcolonies form on cell surface (more sophisicated than clumping, often in invasion form microcolonies prior to invasion)

Question 11

gram positive pili overview

Answer 11

important in:
bacterial adhesion, colonization, biofilm formation, translocation across host membranes and invasion of host tissues

anchored to peptidoglycan

covalent linkage between subunits

example:
zippering in streptococcus

Question 12

secretion is an important…

Answer 12

virulence mechanism

Question 13

secretion

Answer 13

implies from the cytoplasm to the external environment

across both membranes in gram negatives

Question 14

translocation

Answer 14

across a membrane

either cytoplasmic or outer membrane

Question 15

three possible fates for secreted molecules

Answer 15

attached to the cell surface

released into the extracellular environment

injected directly into a host cell (effector proteins)

Question 16

functions of secreted proteins

Answer 16

1. cell shape and stability
   - biogenesis of cell envelope
2. nutrient acquisition
   - degradative enzymes
3. sensing/responding to environment
4. motility
   - flagella, pili etc
5. intercellular communication
6. virulence factors
   - exotoxins, effector proteins, protein adhesions

Question 17

gram negative bacteria adhesion
- Neisseria gonorrhoeae

Answer 17

urogenital pathogen

cause of gonorrhoea (STD)

females
- mild vaginitis
- complications: pelvic inflammatory disease, sterility

males:
- painful infection of the urethral canal

Question 18

architecture of the type 4 pilus
(gram negative)

Answer 18

flexible
central pore 1.2nm (structural phenomenon)
overall diameter 5-6nm
pilins have a highly conserved hydrophobic N-terminus
EPEC Neisseria gonorrhoeae

Question 19

adhesion in Nesisseria

Answer 19

neisseria have type IV pilus and opacity-associated proteins (opa)
primary anchorage is via type IV pilus
type IV pili retract to bring bacteria closer to surface
tight secondary adherence opas bind to host cell receptors

Question 20

twitching motility: N. gonorrhoeae
- role in pathogenesis

Answer 20

adhesion (brings other adhesins close to their target)
microcolony formation
mechanical force generated may have a role in signal transduction

Question 20

twitching motility: N. gonorrhoeae

Answer 20

pilus is extended
- assembly ATPase

pilus attaches to host epithelium
- receptors

pilus is retracted causing movement
- retraction ATPase
- 1 um per sec

Question 21

enteropathogenic E.coli (EPEC)
- overview

Answer 21

causes diarrhoea
colonises the gut epithelium
Type 4 pilus involved in the first stage of attachment
attaching and effacing lesions:
- effector proteins and intimin
- secretion via a T3SS
host cells from pedestals
- host actin cytoskeleton remodelled

Question 22

EPEC pathogenesis

Answer 22

BFP (type 4 pilus) for attachment to enterocytes

adhesion via type 3 secretion system (T3SS)

T3SS injects “effectors” into the host cell
- including the receptor tir, becomes located in host cell membrane
- other effectors interact with host cytoskeleton proteins

pedestal formation
- Intimin (bacterial adhesin) binds to tir (receptor)
- cytoskeleton rearrangements ive rise to pedestal and loss of microvilli