Tropheryma whipplei
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Sadaf Sharfaei M.D.[2]
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| Tropheryma whipplei La Scola et al 2001 |
Overview
Tropheryma whipplei is a bacterium and the causative organism of Whipple's disease.[1] While T. whipplei is categorized with the Gram-positive Actinobacteria, the organism is commonly found to be Gram-negative or Gram-indeterminate when stained in the laboratory.[1] Whipple himself probably observed the organisms as rod-shaped structures with silver stain in his original case,[2] but no name was given to the organism until 1991 when the name Tropheryma whippelii was proposed after sections of the bacterial genome were sequenced.[3] The name was changed to Tropheryma whipplei in 2001 (correcting the spelling of Whipple's name) after deposition in bacterial collections.[1]
Description
Tropheryma whipplei is a gram-positive rod-shaped bacterium. It was finally isolated in eukaryotic cells in the year 2000 and propagated in a culture at 37 degrees Celsius, but was believed to resist culturing for a long time. In fact, it still can only be cultured if part of its eukaryotic host is present. The isolation from human cells and the culturing has allowed more characterization, including sequencing its genome that has resulted in 808 predicted protein-coding gene sequences, even though it grows at a very slow rate of about 4 to 17 days. It is mesophilic, meaning it grows best at moderate temperatures ranging between 25 and 40 degrees Celsius. Its optimal temperature is 37 degrees Celsius. However, Tropheryma whipplei has a special ability as even though it is not affected by heat shock, it can modify its transcriptome following cold shock at a temperature of 4 degrees Celsius; this proves that although it lacks a lot of typical regulatory elements, it still has a highly adaptive response to thermal stresses that would be typical with its potential environmental origin being that of something probably at lower temperatures (something still being studied), thereby allowing it to live and adapt in cold conditions.
Structure
Genome structure
Tropheryma whipplei has a 0.92 Mb genome, placing it in a high-G+C-content gram-positive bacterial group. it is the only known human pathogen with a reduced genome sequence within the class of Actinobacteria. This means that this pathogen is the smallest known within its class. It is a reduced genomic species and it does not have many genes regulating transcription. It has a circular genome of 927,303 base pairs. Tropheryma whipplei has a low G+C content at 46%. Yet, it was originally considered high because 552/808 identified Open Reading Frames have their closest homologs within other actinobacteria class genomes. An ORF is important to determine once a gene has been sequenced, as it deals with where the encoded proteins are first transcribed into messenger RNA and then translated into a protein. A particular nucleotide will start and another will stop (known as a stop codon) translation; this is an ORF. Due to its small genomic size, much has yet to be discovered.
Cell structure
Ecology
Tropheryma whipplei is suspected to have an environmental origin because its closest known relatives originated from the soil. However, Tropheryma whipplei is solely dependent on humans. Tropheryma whipplei inside its host is constantly reshaping itself and invade other organs. The fact that it is also very difficult to cultivate without human cells, makes understanding this pathogen harder.
Natural Reservoir
Pathogenesis
References
- ↑ 1.0 1.1 1.2 {La Scola B, Fenollar F, Fournier P, Altwegg M, Mallet M, Raoult D (2001). "Description of Tropheryma whipplei gen. nov., sp. nov., the Whipple's disease bacillus". Int J Syst Evol Microbiol. 51 (Pt 4): 1471–9. PMID 11491348.
- ↑ Whipple GH. (1907). "A hitherto undescribed disease characterized anatomically by deposits of fat and fatty acids in the intestinal and msenteric lymphatic tissues". Johns Hopkins Hosp Bull. 18: 382&ndash, 91.
- ↑ Relman D, Schmidt T, MacDermott R, Falkow S (1992). "Identification of the uncultured bacillus of Whipple's disease". N Engl J Med. 327 (5): 293–301. PMID 1377787.