Iron And Motility

Question 1

A ‘pathogen’ must be able to:

Answer 1

•attach to host cells for colonisation
•evade or survive the host immune response, and then persist
•obtain iron and other nutrients
•invade and disseminate within host
•produce disease symptoms
•be released and spread to other hosts

Question 2

Why do nearly all bacteria require iron?

Answer 2

•iron is a central trace element in cellular respiration
•found in cytochromes, iron-sulfur proteins
•co-factor in enzymes

Question 3

Iron deprivation

Answer 3

Bacteriostatic

Question 4

Extreme iron deficiency

Answer 4

Bactericidal

Question 5

An example of an organism that doesn’t require iron for growth

Answer 5

Borrelia burgdorferi (Lyme disease)

Question 6

What does Borrelia burgdorferi use instead of iron?

Answer 6

Manganese, because it lacks iron-dependent enzymes

Question 7

What’s a virulence factor of Borrelia burgdorferi?

Answer 7

Iron abstinence

Question 8

Name 3 iron-binding proteins in mammalian hosts

Answer 8

•transferrin
•lactoferrin
•haemoglobin

Question 9

Transferrin

Answer 9

Made in the liver, a serum protein responsible for iron transport in blood and tissues

Question 10

Lactoferrin

Answer 10

A protein secreted at mucosal surfaces, found in milk, saliva, tears

Question 11

Haemoglobin

Answer 11

Contains heme, 70% of the body’s iron is in RBCs

Question 12

Haemolysin source of iron

Answer 12

•heme
•pathogens lyse RBCs via haemolysin, digests haemoglobin, assimilates heme (contains iron)

Question 13

Streptococcus pneumoniae iron virulence

Answer 13

•uses pneumolysin
•binds to cholesterol in host cell membrane
•forms pores in membrane

Question 14

Escherichia coli iron virulence

Answer 14

•systemic E coli (in the body) produces alpha-haemolysin
•faecal E coli (non-invasive) do not

Question 15

Iron source for siderophores

Answer 15

Transferrin and lactoferrin

Question 16

How do siderophores ‘steal’ iron?

Answer 16

•low molecular weight compounds
•chelate iron
•have higher affinity to iron than host proteins

Question 17

What are the 2 main types of siderophores?

Answer 17

•catechols
•hydroxamates

Question 18

Give an example of a catechol

Answer 18

•enterobactin in E. coli
•forms a trimer, containing 3 Fe3+

Question 19

Give an example of a hydroxamate

Answer 19

•aerobactin in E. coli

Question 20

How do siderophores work

Answer 20

•siderophore secreted from T1SS via TolC channel into host
•complexes with Fe3+, removing it from host due to higher affinity
•iron-siderophore complex taken into cell via specific transport mechanism
•ferric reductase reduces Fe3+ -> Fe2+
•Fe2+ has reduced affinity for siderophores, and is released
•non-reusable siderophores are degraded to release iron

Question 21

Siderophore transport into cell using FeENT (ferric enterobactin) as example

Answer 21

•TonB, located in periplasm, rotates due to the proton motive force which occurs in the IM
•TonB rotation promotes a conformational change in the OM transporter
•this allows FeENT to pass through the OM, into the periplasm, and then into the inner/plasma membrane
•an ABC transporter is located in the IM and takes FeENT into the cell

Question 22

Give an example of a species that is still virulent without siderophores

Answer 22

Vibrio cholerae

Question 23

How do siderophore-negative mutant V. cholerae acquire iron?

Answer 23

•they encode uptake systems for both ferrous and ferric iron without need for siderophore
•ferrous iron can diffuse across OM via porin channels

Question 24

Aerobactin

Answer 24

•induced rapidly (early stages of infection)
•lower (less efficient) Fe affinity
•re-usable

Question 25

Enterobactin

Answer 25

•induced slowly (when infection is established) •has higher Fe affinity •not re-usable, is degraded

Question 26

What are the iron sources for direct contact?

Answer 26

Transferrin and lactoferrin

Question 27

How does direct contact work?

Answer 27

•specific receptors on bacterial surface bind to transferrin/lactoferrin of host they infect •Haemophilus influenzae is a human pathogen, it binds directly to human transferrin

Question 28

Transferrin binding protein A (TbpA)

Answer 28

•outer membrane protein (OMP) •TonB dependent transporter •binds non/ferrated transferrin with equal affinity •pore through which iron enters the cell

Question 29

Transferrin binding protein B (TbpB)

Answer 29

•surface lipoprotein •binds only to ferrated transferrin (increases efficiency of iron uptake by TbpA) •grabs iron-loaded transferrin and brings it close to TbpA

Question 30

FbpA

Answer 30

•ferric binding protein •periplasmic transport for iron

Question 31

FbpB

Answer 31

•permease •plasma membrane transport of iron •an ABC transporter

Question 32

FbpC

Answer 32

•an ATPase •provides energy for plasma membrane transporter

Question 33

Counterclockwise rotation

Answer 33

Produces run motion

Question 34

Clockwise rotation

Answer 34

Produces tumble

Question 35

Chemotaxis without a nutrient gradient

Answer 35

•random walk •run followed by tumble •next run in a random direction

Question 36

Chemotaxis with a nutrient gradient

Answer 36

•biased random walk •positive/negative chemotaxis When moving towards nutrient: •fewer tumbles, longer runs When moving away from nutrient: •more tumbles, shorter runs

Question 37

Helicobacter pylori motility

Answer 37

•have tuft of 4-7 flagella •spiral cells, corkscrew motion through viscous fluids •flagella negative (Fla-) unable to colonise (demonstrates motility as a virulence factor)

Question 38

Vibrio cholerae motility virulence

Answer 38

•infect small intestine; watery diarrhoea, vomiting, dehydration •comma shaped, single polar flagellum •during proliferation, flagella is lost and toxin production begins •Fla- have reduced virulence •Fla+ that rotate CW (tumble only) have reduced virulence •Fla+ that rotate CCW (run only) have increased virulence

Question 39

V cholerae stages of infection

Answer 39

1. Bacteria enter GI tract •bile in lumen keeps virulence genes OFF, but enhances motility •2 component transcriptional regulatory system 2. Bacteria swim into mucous •bile concentration reduced: virulence genes ON, motility decreased 3. Bacteria produce TCP pilus adhesins, bind to epithelial cell bb and secrete cholera toxin •non-chemotactic mutant (CW rotation) enters mucous but can't directly swim towards epithelial surface •non-motile mutant passes through host without colonising