lecture 7

Question 1

define the type 1 fimbriae

Answer 1

well characterised fimbrial system
it’s an important of virulence factor in a range of pathogens like e-coli
it is thin 7 nanometres wide and 2 micrometres long surface polymer
the bulk is made up of 500 to 3000 subunits of the protein FimA stacked in a helical cylinder

Question 2

Fim proteins of fimbriae type 1

Answer 2

FimH is the tip adhesin and it binds to d mannose containing structures
FimF and FimG link FimH onto the fimbriae

FimC chaperone export system
FimD usher protein (catalyses FimA polymerisation at base of pili)

Question 3

define PAP

Answer 3

P-pili, P-fimbriae, PAP (Pyelonephritis Associated Pili)
critical virulence factor of uropathogenic e-coli which causes cystitis and pyelonephritis. pap is specifically adapted to the urinary tract to cause infections

it is similar in structure and assembly to type 1 fimbriae
PapG is the tip adhesin (PapG1 PapG2 PapG3)

Question 4

define type IV pili

Answer 4

it is mostly in gram negatives (some in gram positive)
it is usually longer than fimbriae up to 10 micrometres
it only has few pili per cell
typically at both cell poles
most are not hollow unlike flagella

Question 5

role of type IV pili

Answer 5

it is thin, has flexible fibres and is very long
aerofin aggregates laterally to form bundles and these bundling mutants lack virulence

ROLES
host cell adhesion 
twitching motility crawl along surface 
biofilm formation 
enable EPEC to form micro colonies on tissue monolayers

Question 6

explain the species specificity of pathogens

Answer 6

many pathogens are species specific
the specificity of e-coli pathogens are determined by LPS (O antigen) and fimbriae (K antigen)

inter species transfer is difficult because the adhesins on the pathogen struggles to find somewhere to stick to on the Host if they don’t match however genes can still transfer

Question 7

explain ETEC strains interactions

Answer 7

enterotoxigenic e coli strains have specific interactions with mucosal epithelium via colonising factor antigen.
non pathogenic strains do not possess CFA. they do not have the antigens that leads to colonisation but they will stick to different parts of the gut
pathogenic strains of here to other tissues much further up and then express their pathogenicity by producing toxins

Question 8

define the f pilus

Answer 8

it is up to 10 nanometres in length and 8 NM in diameter
it is unlike other pili and fimbriae. they have a central 2 nm wide channel
they are found on many gram negative bacteria, all the plasmid is encoded and there are currently over 20 types characterized
they’re all involved in transfer of genetic information

Question 9

define the sex pilus (e coli F pilus)

Answer 9

it is required for gene transfer
helical arrangement of pilin TraA
in acts like type IV pili in adhesion by attaching via the tip and retracting to bring the cells closer

Question 10

describe the four steps of conjugation

Answer 10

1. donor cell attaches itself to a cell that doesn’t have an f pilus
2. retraction pulls the cells close together
3. exchange happens where the f plasmid gets transferred through a joint between the two cells
4. transformation of curves so that both become f + cells

Question 11

define bacterial endospores

Answer 11

it is the dormant stage in a bacterial life cycle for them to survive different conditions
endospores can survive difficult conditions and they are different to exospores in fungi which can spread
they form inside of the bacterial cell and they can last very long
they can act as a dispersal stage of the organism where they are dispersed through wind water and faeces to find a host cell

Question 12

when do bacterial endospores form?

Answer 12

they form when a vegetative cell becomes stressed
when stressed it produces a very resistant endospore which waits and disperses until conditions get better and produces new vegetative cells

GRAM POSITIVE BACTERIA PRODUCE ENDOSPORES

Question 13

shape and visualisation of endospores

Answer 13

they can be terminal or subterminal, oval or spherical
some cause cell wall to bulge
spore stain is malachite green, white in gram stain cells

Question 14

define the process of sporulation

Answer 14

it is a complex series of cellular differentiation events composed of several stages each controlled by different genes
the process takes 8 hours and it’s a commitment by the cell to become something completely different
the cell stops doing what it normally does and only focuses on sporulation which can be triggered by growing spores bacteria (trigger like nutrient depletion)

Question 15

stages of sporulation (4)

Answer 15

0. when the vegetative cell recognises it is under stress
1. DNA is arranged along the cellular axis
2. a genome copy enclosed in forespore septum, forespore produced by membrane invagination. this means it puts a genome copy in one end of the cell and seals it off to form a forespore sector
3. the cell membrane engulfs the forespore in a second membrane
4. the Cortex between membranes accumulates calcium and acid to become dehydrated and resistant to chemicals and heat
5. complex exosporium layers are produced. often matures with sticky layers
6. the spore matures with complete cortical layers
7. the original cell lysis, dies and releases the spore

Question 16

explain the structure and resistance of endospores

Answer 16

it has many new layers the outermost layer is exosporium which is a thin layer of proteins
then it has spore coats consisting of proteins to survive under harsh conditions
then the peptidoglycan cortex
then the core which contains the genome cytoplasm and ribosomes but is metabolically inactive

spores are metabolically inactive because they are dehydrated so that the proteins and DNA are protected but they can’t function normally
sports will slowly Decay over time if we maintain them at high temperatures above 150 degrees
new proteins are produced that maintain the integrity of the DNA and prevent the formation of pyrimidine dimers which are affected by UV lights

Question 17

define and explain germination

Answer 17

the uptake of water and amino acids act as trigger’s for complete germination
germination is a rapid process of 30 minutes
as it rehydrates, it becomes sensitive to chemicals and heat again, the cell is released and begins to grow in a normal way
usually gram negative cells are released but as the peptidoglycan layer is rapidly built up they become gram-positive again

Question 18

what is the biggest cause of death in the West?

Answer 18

bacterial eukaryotic and viral infections cause deaths more than heart diseases or cancer
of these diseases we have effective treatments to the moon but not everyone has access to them