Lecture 7. Bacterial Cell Envelope Part 2. Flashcards
What is beyond the outer membrane and cell wall ?
- Capsules, EPS and biofilms
- S-layers
- Fimbriae and pili
What does EPS stand for ?
Extra cellular polysaccharides
What do capsules, EPS and biofilms have in common ?
- Outermost layer of protection
- Common structure, biogenesis and export pathways
- Assists in adhesion and solid surfaces
- Protects against antibiotics, antimicrobial peptides and host immune responses
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Where are capsule polysaccharides retained ?
On cell surfaces
What happens to EPS ?
They are secreted
What happens to biofilms ?
Product of multiple extra cellular bacteria producing EPS
What is a capsule ?
A type of glycocalyx
What is meant by distinct, gelatinous ?
Capsule
What is meant by slime layer ?
Irregular, diffuse
What does a capsule have in terms of water ?
High water content
What is the capsule important for ?
Virulence – resists phagocytosis
What is the function of capsule ?
- Barrier to toxic hydrophobic molecules
- Protection against dessication
- Resistance to bacteriophage
- Evade host defences
What does a capsule that avoids detection do ?
Hide surface structures – resist phagocytosis
What does a capsule do to avoid destruction ?
Prevent complement-mediated lysis
Where are opsonins directed to ?
Cell envelope components are deposited beneath the capsule layer
What is an opsonin ?
Substances that bind to foreign micro-organisms making them more susceptible to phagocytosis
What does capsule do to opsonin ?
Inhibits access
What often are invasive bacterial pathogens ?
Encapsulated
What are EPS important for ?
The structure and function of biofilms
What are bacteria in biofilm ….
- Impervious to phagocytosis by neutrophils and macrophages
- Resistant to antimicrobial peptides and complement
- Semi-dormant - difficult to inhibit with antibiotics
What are biofilm associated infections ?
- S. aureus
2. S. epidermis
What does Pseudomonas aeruginosa biofilms do ?
Cause cystic fibrosis in lung infections
What is a s-layer ?
Extracellular layer coating the entire bacterial cell surface
Where are s-layers found ?
- Gram positive bacteria
- Gram negative bacteria
- Archaea
What are s-layers composed of ?
Protein or glycoprotein
What is the structure of s-layer ?
- Protein subunits come together to form selection of arrays
- Porous mesh
- Protective barrier
- Selective permeability
What are the functions of s-layer ?
- Molecular sieve
- Protection
- Adherence to host cell surfaces
What are pili made of ?
Pilin protein
What are the two types of pili ?
- Sex pili
2. Ordinary pili
What do pili do ?
- Attach to other bacteria
2. Motility
Where are pili mostly found ?
Gram negative bacteria
What type of pili are found in P. aeruginosa ?
Type 4 pili
What do type 4 pili do ?
- Adherence to surfaces
- Biofilm formation
- Twitching motility
- Senses initial contact with surfaces
What are fimbriae ?
Bristle like fibers present in large numbers
What do fimbriae do ?
Help attach cells to a solid surface or tissues
What do fimbriae do to bacteria?
Help bacteria cling together
Where are fimbriae found ?
Gram negative and gram positive
Where do fimbriae recognise host molecules ?
Adhesin present at tip
What is the structure of fimbriae in E.coli ?
- FimH tip protein - adhesin
- 3nm thick tip fibrillum composed of 2 proteins
- 7nm thick helical rod–subunits of fimA
What are virulence factors during bladder infection ?
Type 1 fimbriae fimH and P fimbriae
Where do fimbria adhere to in bladder infection ?
Uroepithelial cells of baldder
What is the receptor in bladder infection ?
Mannose containing glycoproteins
