16 - Iron Uptake & Motility Flashcards
1
Q
Bacterial virulence factors
A
Molecules produced by bacteria, or strategies used by bacteria to cause disease
2
Q
Pathogens must be able to
A
- Attach to host cells for colonisation
- Evade host immune system
- Obtain nutrients (e.g. iron)
- Spread within host (some)
- Produce disease symptoms (to be considered pathogen)
- Spread to other hosts (survival of species)
3
Q
Iron acquisition as bacterial virulence factors
A
- Nearly all bacteria require iron for growth
- Iron deprivation is bacteriostatic, extreme deficiency is bactericidal
4
Q
Why do bacteria require iron for growth
A
Iron is a central trace element in respiration and a cofactor in many enzymes
5
Q
Example of genera that don’t need iron for growth
A
Borrelia burgdorferi (Lyme disease)
6
Q
Iron in mammalian hosts
A
Tightly sequestered by iron binding proteins
7
Q
Three iron binding proteins
A
- Transferrin (made in liver, the serum protein responsible for iron transport)
- Lactoferrin (protein secreted at mucosal surfaces, found in milk, salvia, tears)
- Hemoglobin (contain heme, 70% of total body iron is in RBCs)
8
Q
Three main mechanisms of iron uptake by bacteria
A
- Hemolysins (iron source = heme)
- Siderophores (iron source = transferrin and lactoferrin)
- Direct contact (iron source = transferrin and lactoferrin)
9
Q
Hemolysins
A
- The pathogen hemolysin lyses erythrocytes, then digests the hemoglobin and assimilates the heme which contains iron
- E.g. Streptococcus pneumoniae (pneumolysin)
10
Q
Pneumolysin
A
Binds cholesterol in host cell membranes and disrupts them by forming pores
11
Q
Steps of heme uptake into bacterial cell
A
- Heme is bound to an OM receptor
- Heme is released to carrier protein in periplasm
- Heme is delivered to an ABC transporter in the inner membrane which uses ATP to import heme into cytoplasm
- Bacterial heme oxygenase degrades heme to release iron
12
Q
Two minor proteins complexed with heme
A
Hemopexin and haptoglobulin
13
Q
Siderophores
A
- Low molecular weight compounds that chelate iron with very high affinity
- Best studied
- Wide spread among species
- Two main chemical types
14
Q
What are the type main chemical types of Siderophores
A
- Catechols (e.g. E. coli enterobactin)
- Hydroxamates (e.g. E. coli aerobactin)
15
Q
How do siderophores work
A
- Siderophore is secreted via T1SS
- Complexes with Fe3+, removing it from host protein due to siderophore’s higher affinity for iron
- iron-siderophore complex taken into bacterial cell
- Iron released from complex as Fe2+ via ferric reductase
16
Q
Release of iron from complex as Fe2+ with non re usable siderophores
A
Siderophore is degraded by protease to release the iron
17
Q
Regulation of siderophore and membrane transport proteins by iron levels
A
- Low iron = synthesised
- High iron = repressed
- As siderophore and iron transport proteins are burden for pathogen to produce
18
Q
Siderophore transport into cell
A
- Energy coupled OM transporters
- Transmission of energy from IM to OM done via TonB protein
19
Q
TonB protein
A
- Rotates
- Rotations powered by PMF, and that promotes conformational change of the OM transporter such that the substrate (feEnt) can pass through ABC transporter in PM
20
Q
Is siderophore production a bacterial virulence factor
A
- Not always
- Loss of ability to produce siderophores is sometimes associated with loss of virulence (e.g. E. coli)
- But Vibrio cholerae siderophore- negative mutants are still virulent
21
Q
Aerobactin
A
- Induced rapidly (early stages of infection)
- Lower Fe affinity (less efficient)
- Re usable
22
Q
Enterobactin
A
- Induced slowly (when infection is established)
- HIgher Fe affinity
- Degraded
23
Q
Direct contact iron uptake system
A
- Bacteria directly bind to host transferrin or lactoferrin
- Mechanism of iron uptake requires a number of membrane proteins
- Bacteria have specific receptors for transferrin or lactoferrin of the hosts they infect
24
Q
Example of bacteria that have specific receptors for transferrin or lactoferrin of the hosts they infect
A
- Haemophilus influenzae
- Human pathogen
- binds human transferrin (not other mammals)
25
Other proteins involved in iron acquisition
- TbpA
- TbpB
- FbpA
- FbpB
- FbpC
26
TbpA
Binds ferrated and non-ferrated transferrin with equal affinity, and is the pore through which iron enters the cell
27
TbpB
Binds only to ferrated transferrin, increases the efficiency of iron uptake by TpbA
28
FbpA
- Ferric binding protein
- Periplasmic transport of iron
29
FbpB
- Permease
- Plasma membrane transport of iron
- ABC transporter
30
FbpC
- ATPase
- PRovides energy for plasma membrane transporter
31
Motility and flagella as bacterial virulence factors
- The capacity to move towards a host surface via chemotaxis could be beneficial to a pathogen
- Motiliity associated with virulence
32
Examples of bacteria that as motility virulence factor
- Helicobacter pylori
- Vibrio cholerae
- Salmonella and Campylobacter
33
Counterclockwise flagella rotation
Produces run
34
Clockwise flagella rotation
Produces tumble
35
Chemotaxis
- Directed movement towards a chemical attractant or away from chemical repellent
- If no attractant or repellent present, motile bacterial cells move in random directions (random walk)
- If attractant or repellent present, cells move in a biased random walk
36
Random walk
Run is followed by tumble, next run is in random direction
37
Biased random walk
- Fewer tumbles, longer runs when moving up gradient towards nutrients
- More tumbles, shorter runs when moving away from nutrient
38
Role of motility in process of ulcer formation by H. pylori
- H. pylori uses urease (urea → ammonia + bicarbonate) to protect it from stomach acid during transit of the stomach to the mucin layer.
- The bacteria are attracted to the epithelial layer and swim down via chemotaxis through the viscous mucin layer.
- They colonize the mucin layer and may adhere to the gastric mucosa.
- Products of the bacteria provoke an inflammatory response that ultimately
damages the mucosa
39
Two results of flagella-positive (Fla+) but non-chemotactic mutants (inactivated sensing system)
1. Flagella rotated clockwise only (cells tumble only), mutant had decreased virulence
2. flagella rotated counterclockwise only (cells run only), mutant had increased virulence
40
Vibrio cholerae motility
- Use flagella to swim through mucous layer to the intestinal wall
- During proliferation at the intestinal wall flagella are lost, toxin production begins
41
Stages of infection in V. cholerae disease
1. Bacteria enter GIT (bile keeps virulence gene expression off)
2. Bacteria swim into mucous gel (low bile --> virulence genes on)
3. Bacteria produce tcp pilus adhesins, bind to epithelial cell brush border and
secrete cholera toxin
42
Non motile cholera mutant
passes through host without colonizing
43
Salmonella spp./Campylobacter spp. adherence
There is a distinction between motility as a virulence factor, and the flagellum as an adhesin virulence factor
