Transcript Salmonella Typhi

Salmonella Typhi
By
Sandy Do
What is it?
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A bacteria
Causes typhoid fever that affects 16
million people annually and causes
600,000 fatalities
Has evolved the ability to spread from the
intestine to the deeper tissues of humans,
including the liver, spleen, and bone
marrow
What is it? Cont…
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Resistant to many drugs
Closely related to Salmonella typhimurium (also
already sequenced), classified under the same
species as Salmonella typhi
Difference is that S. typhi causes typhoid fever
and can only infect humans, whereas S.
typhimurium causes food poisoning and can
affect almost all animals
Where and When?
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Sequenced by the Sanger Institute
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On November 7, 2001
Why?
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It affects millions of people and
sequencing the genome can help us find a
way to block its transmission in humans,
eradicating it altogether
Can help improve diagnostic tools and
vaccines
Why?
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Multiple drug resistance (MDR) is a
emerging problem in treating infectious
diseases
Salmonella typhi is one example of MDR
microorganism
It is resistance to fluoroquinolones, the
most effective antimicrobials for the
treatment of typhoid fever
So…..?
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Since salmonella typhi is an example of an
emerging MDR microorganism, studying
this genome can contribute to the
understanding of how such
microorganisms adapt rapidly to new
environmental changes that are presented
by modern human society.
Some Statistics
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Chromosome sequence is 4,809,037 bp in
length
C+G content of 52.09%
4,599 protein-coding genes (402 of these
are pseudogenes)
Side Note:
Pseudogene: once functional stretches of
DNA that have been inactivated by
mutation
Some Results
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The genome shows hundreds of deletions
and insertions, resulting in MDR
Found the plasmid in Salmonella typhi that
encodes resistances to all of the first-line
drugs used for the treatment of typhoid
fever
Many other genes responsible for
resistance in drugs were indentified
Side Note
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Plasmid: A piece of symbiotic DNA, mostly
in bacteria but also in yeast, not forming
part of the normal chromosome DNA of
the cell and capable of replicating
independently of it. Plasmids carry a
signal situated at their replication origin
dictating how many copies are to be
made, and this number can be artificially
increased.
Results Cont…
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Salmonella typhi’s genome gives us hints
as to why it only infects humans
Because it has 204 pseudogenes. Working
versions of these genes were discarded
during typhi’s evolution for its current
habitat in humans
Vs. typhimurium only has about 40
pseudogenes
Results Cont…
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Both typhi and typhimurium have
hundreds of genes that are different. This
is very surprising because these two
organisms are classified as a single
species
Bibliography
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The Wellcome Trust Sanger Institute Website:
http://www.sanger.ac.uk/Projects/S_typhi/
Thain, M., Hickman, M. The Penguin Dictionary of Biology. New York:
Penguin Books, 2000
Whitfield, John. (2001, October 25) “Salmonella Bacteria Sequenced”
[Article posted on website]
http://www.nature.com/nsu/011025/011025-10.html
“Complete Genome Sequence Of A Multiple Drug Resistance Salmonella
enterica serovar Typhi CT18”
http://www.nature.com/cgitaf/DynaPage.taf?file=/nature/journal/v413/n6858/full/413848a0_fs.html
“Complete genome sequence of Salmonella enterica serovar Typhimurium
LT2”
http://www.nature.com/cgitaf/DynaPage.taf?file=/nature/journal/v413/n6858/full/413852a0_fs.html