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Salmonella Typhi

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Title: Salmonella Typhi


1
Salmonella Typhi
  • By
  • Sandy Do

2
What is it?
  • 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

3
What is it? Cont
  • 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

4
Where and When?
  • Sequenced by the Sanger Institute
  • On November 7, 2001

5
Why?
  • 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

6
Why?
  • 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

7
So..?
  • 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.

8
Some Statistics
  • Chromosome sequence is 4,809,037 bp in length
  • CG content of 52.09
  • 4,599 protein-coding genes (402 of these are
    pseudogenes)

9
Side Note
  • Pseudogene once functional stretches of DNA that
    have been inactivated by mutation

10
Some Results
  • 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

11
Side Note
  • 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.

12
Results Cont
  • Salmonella typhis genome gives us hints as to
    why it only infects humans
  • Because it has 204 pseudogenes. Working versions
    of these genes were discarded during typhis
    evolution for its current habitat in humans
  • Vs. typhimurium only has about 40 pseudogenes

13
Results Cont
  • 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

14
Bibliography
  • 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.htm
    l
  • Complete Genome Sequence Of A Multiple Drug
    Resistance Salmonella enterica serovar Typhi
    CT18
  • http//www.nature.com/cgi-taf/DynaPage.taf?fil
    e/nature/journal/v413/n6858/full/413848a0_fs.html
  • Complete genome sequence of Salmonella enterica
    serovar Typhimurium LT2
  • http//www.nature.com/cgi-taf/DynaPage.taf?f
    ile/nature/journal/v413/n6858/full/413852a0_fs.ht
    ml
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