Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
38 Cards in this Set
- Front
- Back
|
What is the difference between pathogenicity and virulence?
|
Pathogenicity is qualitative: yes or no ans
Virulence: Quantitative, can be +1 virulence, or +2 etc |
|
|
How is virulence defined?
|
Depends on point of reference
M. tb is more virulent for humans than cows (if put it in cows, they're vaccinated vs M. bocis) M. bovis is more virulent for cows than humans |
|
|
Can M. bovis harm ppl?
|
Yes, but mostly only immunocompromised ppl (ppl with AIDS)
|
|
|
Which is more virulent: bovis or tb?
|
Bovis more virulent for wider species. Also infects mice and rabbits, unlike TB
TB also infect guinea pigs |
|
|
How is virulence studied?
|
-Biohazard: lvl 3, highly transmissible, but treatable (TB) or low transmittance, but untreatable (AIDS)
|
|
|
What are some problems with studying virulence?
|
Slow generation time (doubling time =24 hours)
Targeted gene disruption is difficult -homologous recombination tricky TB KO= mouse KO Takes 6-9 months to make it |
|
|
What are some animals used?
|
Humans (least easy to use, but most relevant)
Monkeys: closest disease to humans, but expensive and ethical issues, need to use a lot to get useful results Rabbits: close in pathology, get cavitary lung lesions, high transmission, bad for handler but good for studying disease, but can't just do KO Mice: easier to work with, help with primary infections Cell culture: easiest, only one cell, .: immunologically simplified |
|
|
What's the problem with wokring with mice or one cell culture?
|
Mice: are we still studying the same disease?
Can study the infection, but not reinfection or transmission Cell culture: use macs cuz TBs live in them Hallmark of M. tb in macs= granuloma, can't study this with only 1 macrophage |
|
|
Describe the BCG vaccine
|
Attenuated mutant
Derived from M. bovis (1908-1921) More than 100 million doses/yr Disease= 1/100, 000 |
|
|
Why is the virus still attenuated after all this time?
|
Attenuation in vitro
Grow bacteria long enough in the lab, it will become attenuated -> Genomics of reduced virulence |
|
|
Compare TB vs BCG
Birthplace |
M. tb: Africa
M. bovis BCG: France |
|
|
Compare TB vs BCG
Birthdate |
TB: Paleolithic
BCG: 3rd Republic (1908) |
|
|
Compare TB vs BCG
Home |
TB: Host mac
BCG: vaccine lab |
|
|
Compare TB vs BCG
Job |
TB: Cause disease
BCG: Prevent disease |
|
|
Compare TB vs BCG
Infected |
TB: 2 billion ppl
BCG: 100 million/year |
|
|
Compare TB vs BCG
Disease |
TB: 1 in 10
BCG: 1 in 100,000 |
|
|
Relatedness
|
>99% genetic identity
v/ similar at genetic level, but very different virulence |
|
|
MICROARRAY
|
LOOK at slide bottom of page 5
Lots of similarity btw TB and BCG |
|
|
How many genes are different btw TB and BCG?
|
16 deletions in BCG that are in TB
These16 deletion code for 129 genes (ORFs) |
|
|
What did these dif deletions code for?
|
4 of these deletions could be difference in TB strains (TB variance)
7 deletions are the dif btw TB (human) and Bovis (parent of BCG) .: difference btw human and cow pathogenesis 1 deletion: present in M. bovis isolate, but missing from all BCG strains |
|
|
What was this 1 last deletion?
|
RD1
Candidate for how BCG lost its virulence btw 1908 and 1921 |
|
|
Where is RD1 present?
|
RD1 is present in virulent bacteria
RD1 is absent in avirulent bacteria RD1 clue to virulence in TB? |
|
|
What is common btw M. microti, M. bovis and Dassie bacillus?
|
All have an independent deletion in RD1
At least btw 3874 and 3876 => 3 genes |
|
|
What are these 3 genes?
|
2 of them are secreted Ag
ESAT-6 CFP-10 (culture filtrate ptn 10) |
|
|
Describe RD1
|
9.5 kb
9 ORFs, none with a known fct 2 secreted Ag |
|
|
What is the goal of BCG attenuation?
|
Delete RD1 from H37Rv by allelic exchange
Look for virulence phenotype If attenuated, explore why |
|
|
What were the reuslts of the RD1 deletion in M. TB?
|
-Dec growth in macs
-Dec destruction of macs -Dec growth in lungs -Dec spread from lungs to spleen -Dec pathology in host => Dec virulence =>RD1 important for virulence |
|
|
What does M. marinum do?
|
Hot tub granuloma in ppl
TB in fish |
|
|
What happened when RD1 was deleted from M. marinum?
|
The bacteria grow in the macs but don't elicit granuloma formation
|
|
|
What happens if RD1 not deleted?
|
Bacteria directs macrophages to aggregate, allowing intracellular spread
|
|
|
Does the virulent strain want to make granulomas?
|
Doesn't turn off system or hide
Attracts the host and uses its signalling |
|
|
Is the bacteria trying to evade the immune system?
|
Not necessarily
Maybe granuloma perfect for bacteria, not host M. TB = intracellular pathogen .: if mac recruits other macs, can infect more cells M. tb could propagate cell to cell in paracrine manner |
|
|
What happens if RD1 disrupted within the region?
|
Can disrupt ESAT-6, the secreted ptn and .: won't make ESAT-6
Can disrupt any of the other genes (1 by 1), would see that ESAT-6 is made, but is NOT secreted Without the other genes, ESAT-6 could never be secreted and would just stay in the bacteria |
|
|
What happens to RD1 secretion when you disrupt outside RD1?
|
Disruption of Rv3616c-3614c genes allows expression of RD1 genes, but no expression of ESAT-6
|
|
|
What happen to secretion in reciprocity?
|
Disruption of RD1 prevents secretion of these other genes
|
|
|
What is CFP-10 thought to be?
|
Chaperone for ESAT-6
4 paralogs for CFP-10, but its the only one that has 7 aa tail (might help with direct secretion) |
|
|
What is the CFP-10 7 aa tail for?
|
Ubiquitin-fusion: might direct export of ubiquitin from bacterial cell
-Infer that CFP-10 directs secretion of ESAT-6 |
|
|
Summary
|
M. tb manipulates IR to initiate host-pathogen dialogue
Process depends oin part on a secretory system -RD1 enables escape from phagosom to cytosol -RD1 enables spread from cell to cell Ultimate effect of this system spans granuloma formation to virulence -Interaction with other virulence determinants also requires further study |
