Lecture 7: Pili/fimbriae and Endospores Flashcards
Tuesday 22nd October
where are type 1 fimbriae widespread in?
Enterobacteriaceae, including most E. coli
Which pathogens is type 1 fimbriae an important virulence factor in?
E. coli
Salmonella spp.
Vibrio cholerae
What is the size of type 1 fimbriae?
7 nm wide and approximately 1-2 µm long surface polymer
What is type 1 fimbriae made up of?
The bulk of type 1 fimbriae is made up of 500-3000 subunits of the protein, FimA, stacked in a helical cylinder
What is the tip adhesin of type 1 fimbriae?
FimH
What does the FimH tip adhesin bind to?
to D-mannose containing structures (we have mannose in many of our cells)
What links FimH adhesin onto type 1 fimbriae?
FimF and FimG
What proteins are associated with the building of type 1 fimbriae itself?
FimC and FimD
What does FimA do?
It hepls build the pili from the base to the top
What proteins catalyse FimA polymerisation?
FimC and FimD
What is another name for P pili?
PAP: Pyelonephritis-Associated-Pili
What is P-pili a critical virulence factor for?
Critical virulence factor of uropathogenic E. coli (UPEC) which cause cystitis and pyelonephritis
Does cystisis cause discomfort, but not a lot of damage?
Yes
Describe pyelonephritis
- Pyelonephritis is a UTI that reaches the kidneys
- Can be fatal
How is P-pili similar to type 1 fimbriae?
Similar in structure and assembly
What is the tip adhesin of P-pili?
PapG, which binds to surface globoside receptors (glycolipid) in uroepithelial cells
What are the 3 variants of PapG?
PapG1, PapG2 and PapG3
Which bacteria is type IV pili most common in?
Gram negatives
Give some examples of gram negative bacteria
- Enterobacteriaceae
- Salmonella enterica
- Pseudomonas aeruginosa
- Legionella pneumophila
- Neisseria gonorrhoeae
- Neisseria meningitidis
- Vibrio cholerae
- some cyanobacteria
can type VI pili be gram positive?
Some can, but they’re mostly gram negative
Give an example of a gram positive type VI pili
Clostridia
Is it true that Type VI pili are typically longer than fimbriae?
Yes (up to 10 µm)
Is it true that there’s only few pili per cell with type VI pili?
Yes (on the order of 1-10)
Are type VI pili typically at both poles of the cell?
Yes
Are type VI pilli hollow?
No, unlike flagella, which are typically very hollow
How do type vi pili move?
Via twitching motility
How thin are type VI pili?
Quite thin. About 6– 8 nm wide
How does type VI pili form bundles?
By aggregating laterally
Why do type VI pili form bundles?
This makes them more pathogenic
What are the roles of type VI pili?
- Host cell adhesion
- Biofilm formation (EPEC)
- Twitching motility, crawl along a surface
- Enable enteropathogenic E. coli (EPEC) to form microcolonies on tissue monolayers
Is it true that many pathogens are only specific to certain species?
Yes
What is the specificty of E coli pathogens determines by?
LPS (O antigen) and fimbriae (K antigen)
When does inter-species transfer occur?
If there is the correct adherence factor present on new host cells
How do Enterotoxigenic E. coli (ETEC) strains interact with mucous epithelium?
Via CFA – colonising factor antigen
Do non-pathogenic strains of e coli possess cfa?
No
What do non-pathogenic strains of E-coli do?
Non-pathogenic strains adhere to colon and are routinely secreted in faeces
What do the pathogenic strains of e coli adhere to?
tissues, e.g. small intestine and urinary tract
how does e coli express its pathogenicity?
by production of toxins
What are the measurements of the F pilus?
up to 10 µm in length and 8 nm in diameter
Unlike other pili/fimbriae , what does the F pilus have?
a central 2 nm wide channel
What type of bacteria is the F pillus usually found on?
Gram negative bacteria
What type of plasmids are the F pili encoded in?
The F pili are encoded in plasmids that can move from one organism to another
During adhesion, what does the Sex pillus act like?
The type VI pili
(Attach via tip
, Retracts to bring cells together
)
What is the sex pilus best known in?
the E. coli F pilus
when was the sex pilus first identified?
in 1960’s
What is the sex pilus required for?
gene transfer
How many sex pili are usually expressed per cell?
1-3 pili
What is the sex pilus made up from?
The helical arrangement of pilin (TraA)
Is the sex pilus an F pilus?
Yes
What is conjugation?
a form of horizontal gene transfer, where genetic material is transferred from one bacterium to another, typically through direct contact.
Describe the conjugation process
- The sex pilus attaches to a specific receptor on the surface of the recipient bacterium. (F+ donor will only bind to F- recipent)
- Once the pilus makes contact, it retracts, pulling the two bacteria closer together.
- A conjugation bridge is formed, through which plasmid DNA (or sometimes chromosomal DNA) is transferred from the donor to the recipient.
- The cells have now both undergone transformation and both become F+ cells
-
Where do bacterial ‘endospores’ get their name from?
The fact that they form inside bacterial cells
How different are bacterial endospores to fungal endospores?
Very different
What are bacterial endospores extremely resistant to?
heat, desiccation and radiation
Is it true that some bacterial endospores can be viable for 100,000 years?
Yes
How can bacterial endospores be dispersed?
through wind, water and faeces
When do bacterial endospores form ?
When a vegetative cell becomes stressed
When may bacterial endospores germinate and produce new vegetative cells?
When conditions become favourable again
What conditions are bacterial endospores mostly found in ?
Soil bacteria
Is it true that the genera of bacterial endospores mostly include Bacillus, Clostridium, Sporosarcina
?
Yes
Do gram positives or gram negatives produce endospores?
Gram positives
What does Clostridium perfringens cause?
Gas gangrene
Describe how bacterial endospores look like under phase contact
- bright refractile inclusions
- Can be terminal or sub-terminal, oval or spherical
- Some cause cell wall to bulge
Which spore formers are important antigens?
Bacillus anthracis
Clostridium botulinum
Clostridium perfringens (causes gas gangrene)
Is it true that sporulation has several stages, each controlled by different genes?
Yes
How many genes are involved in sporulation?
More than 200
How many hours does sporulation take to complete?
Around 8 hours
What causes sporulaiton genes to be switched on?
- Environmental trigger stops production of normal cell growth proteins and switches on sporulation genes
- Trigger is probably nutrient depletion
Stages of sporulation
- Vegetative cell makes sure that it has 2 copies of its DNA (one to go into the spore and one to survive in the cell)
- Invaginations in cellular membrane
- DNA is organised along its long axis
- Encloses one copy of the DNA into a forespore septum (section of the cell produced by the invaginations).
- Cell membrane engulfs forespore in a second membrane
- The cell dehydrates the inside of the spore by filling it with calcium and dipicolinic acid. This makes the spore very resistant to heat and to chemical attack.
- To make the spore more robust to physical damage, complex exosporium layers are produced on its outside
- A layer of cortex is produced on the outside of the spore to allow the spore to stick to surfaces, like soil particles and animal skin
- Original cell lyses releasing spore
What is the outer most layer of a spore, the exosporium, used for?
Not essential for survival but maybe for dispersal
What does the spore coat consist of?
spore-specific proteins
What does the core of an endospore include?
containing genome, cytoplasm, ribosomes, but metabolically inactive
Why do the endospores need to be dehydrated?
To prevent denaturation
What temperatures can endospores withstant?
150 degrees celcius
What maintains the genome integrity and prevents the formation of pyrimidine dimers in DNA?
Small acid soluble proteins
IS there any discernable metabolic activity inside the spore?
No
What triggers germination in endospores?
Uptake of water and amino acids
How long does germination take?
Rapid process, complete in 30 mins
During germination, when a cell is released, does it begin to grow in a normal way?
Yes and the cell will usually be Gram negative on release but as peptidoglycan layer is rapidly built up they become Gram positive again
What do more people in the world die from, infectious disease, or heart disease or cancer?
Infectious disease
In 2002, how many deaths worldwide were attributable to infectious disease?
In 2002, 14.9 million deaths world wide were attributable to infectious disease
In Africa over 50% of all deaths in 2016 were due to infectious diseases
Compares to only 10% in all of the Americas
What is one of the most devastating infectious diseases humans have suffered from?
The Black Death – Bubonic Plague
When were there pandemics of the plague in Asia and Europe?
In the mid 14th century
What percentage of the european population was the plague said to have wiped out in the middle ages?
Believed to have wiped out between 30-60% of European population in the middle ages, which was about t 1 in 6 of the world’s population at that time (Equivalent to 1 billion people today
)
What is the causative agent of the bubonic plague?
Yersinia pestis, transmitted by rodent populations carrying rat fleas
(Some scientists dispute this saying it moved too quickly across the world
)
What is the energy for flagellar rotation derived from?
The proton motive force
Are the genes for flagellin highly conserved between bacteria species?
Yes
What does the energy required to catalyse the activity of type IV pili come from?
ATP hydrolysis
How does twitiching motility in type IV pili occur?
- Pili extend from one pole of the cell, attach to a surface, and then retract to pull the cell forward.
Are twiching and glilding motility indepnedent of flagella?
Yes, and requires pili
Does gliding motility require flagella or pili?
no
What do bacteria with polar flagellum do instead of tumbling?
They swim backwards, as they can’t form a tuft of flagella and therefore, can’t tumble
