Yersinia pestis infection Microchapters
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Yersinia pestis (Y. pestis), a rod-shaped facultative anaerobe with bipolar staining (giving it a safety pin appearance) causes the infection in mammals and humans. The bacteria maintain their existence in a cycle involving rodents and their fleas. The genus Yersinia is gram-negative, bipolar staining coccobacilli, and, similarly to other Enterobacteriaceae, it has a fermentative metabolism. Y. pestis produces an antiphagocytic slime. The organism is motile when isolated, but becomes nonmotile in the mammalian host.
Yersinia pestis is a nonmotile, non-spore-forming, Gram-negative, non-lactose fermenting, ovoid and "safety-pin-shaped" (bipolar appearance when stained) bacillus. It is an enterobacteriaceae commonly measuring 0.75x1.5 μm. On cell cultures, it grows on sheep-blood agar, as grayish translucent colonies. It also grows on MacConkey and nutrient-rich broths.
Yersinia pestis is thought to have evolved from Yersinia pseudotuberculosis about 1500 - 2000 years ago. According to its behavior towards nitrate and glycerol, Yersinia pestis may be classified as:
- Biovar Antiqua
- Nitrate reduction: positive
- Glycerol reduction: positive
- Biovar Medievalis
- Nitrate reduction: negative
- Glycerol use: positive
- Biovar Orientalis
- Nitrate reduction: positive
- Glycerol use: negative
As of 2006, the genomic sequence of a strain of biovar Antiqua has been completed. Similar to the other pathogenic strains, there are signs of mutations causing loss of function. The chromosome of strain KIM is 4,600,755 base pairs long; the chromosome of strain CO92 is 4,653,728 base pairs long.
Similarly to other enterobacteriaceae (Yersinia pseudotuberculosis and Yersinia enterocolitica), Yersinia pestis is host to the plasmid pCD1. In addition, it also hosts two other plasmids, pPCP1 (also called pPla or pPst) and pMT1 (also called pFra) that are not carried by the other Yersinia species.
- pFra codes for a phospholipase D that is important for the ability of Yersinia pestis to be transmitted by fleas.
- pPla codes for a protease, Pla, that activates plasminogen in human hosts and is a very important virulence factor for pneumonic plague.
- Bacterial adhesion
- Injection of proteins into the host cell
- Invasion of the host cell (via a Type III secretion system)
- Acquisition and binding of iron from red blood cell, via siderophores
A comprehensive and comparative proteomics analysis of Yersinia pestis strain KIM was performed in 2006. The analysis focused on the transition to a growth condition mimicking growth in host cells.
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- "Public Health Image Library (PHIL)".