Lecture 6: Bacterial Cell Envelope Part 2

Question 1

What is beyond outer membrane and cell wall?

Answer 1

1. Capsules, EPS, biofilms -> fortress
2. S-layers -> chainmail
3. Fimbriae and pili -> adhesion

Question 2

Describe capsules, EPS and biofilms

Answer 2

Outermost layer of protection
Common structure, biogenesis and export pathways
Assists in adhesion to solid surfaces
Protects against antibiotics, antimicrobial peptides and host immune responses
Makes infections hard to treat

Question 3

What is EPS

Answer 3

Extracellular polysaccharides

Question 4

Describe capsule

Answer 4

Type of glycocalyx - sticky sugar coat
Distant gelantinous = capsule
Irregular, diffuse = slime layer
High water content
Important for virulence - resists phagocytosis

Ex- Bacillus Anthracis - anthrax

Question 5

Function of a Capsule

Answer 5

Barrier to toxic hydrophobic molecules i.e. detergents
Protect against desiccation
Resistance to bacteriophage
Evade host defenses

Question 6

What is opsonins?

Answer 6

Substance that bind foreign microorganisms that make them more susceptible to phagocytosis

Question 7

Describe EPS and biofilms

Answer 7

Attachment - cell cell adhesion - proliferation - maturation

Ex- Pseudomonas aeruginosa

Question 8

What is S-layer?

Answer 8

Surface layers - extracellular layer coating entire bacterial cell surface
Composed of protein or glycoprotein
Usually single protein

Question 9

Function of S-layer

Answer 9

1. Molecular sieve - cut off determined by size and pores
2. Protection - resistance to bacteriophage, complement, phagocytosis, extreme environment
3. Adherence to host cells and surfaces

Question 10

Describe Pili

Answer 10

Longer, fewer and thicker tubes
Made of pilin protein
Sex pili and ordinary pili
Attach to other bacteria
Motility - crawling/twitching
Mostly Gram-neg

Question 11

Example of Pili

Answer 11

Type IV pili in P. aeruginose
Adherence to surfaces
Biofilm formation
Twitching
Senses initial contact with surfaces

Question 12

Describe Fimbriae

Answer 12

Bristle like small fibres present in large numbers
Help attach cells to solid surface or tissues
Help bacteria cling together
Gram- pos and neg
Adhesion present at tip and recognises host molecules

Question 13

Structure of Fimbriae in E.coli

Answer 13

FimH tip protein - adhesion
3nm thick tip fibrillum composed of 2 proteins
7nm thick helical rod