Salmonella Typhi

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Salmonella Typhi

• By
• Sandy Do

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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

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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

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Where and When?

• Sequenced by the Sanger Institute
• On November 7, 2001

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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

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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

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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.

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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)

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Side Note

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

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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

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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.

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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

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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

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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