Yersinia

Yersinia is a genus of bacteria in the family Enterobacteriaceae. Yersinia are Gram-negative rod shaped bacteria, a few micrometers long and fractions of a micrometer in diameter, and are facultative anaerobes. Some members of Yersinia are pathogenic in humans; in particular, Y. pestis is the causative agent of the plague. Rodents are the natural reservoirs of Yersinia; less frequently other mammals serve as the host. Infection may occur either through blood (in the case of Y. pestis) or in an alimentary fashion, occasionally via consumption of food products (especially vegetables, milk-derived products and meat) contaminated with infected urine or feces.

Speculations exist as to whether or not certain Yersinia can also be spread via  protozoonotic mechanisms, since Yersinia are known to be facultative intracellular parasites; studies and discussions of the possibility of amoeba-vectored (through  the cyst form of the protozoan) Yersinia propagation and proliferation are now in progress.

Microbial physiology
An interesting feature peculiar to some of the Yersinia bacteria is the ability to not only survive but actively proliferate at temperatures as low as 1-4 degrees Celsius (e.g., on cut salads and other food products in a refrigerator). Yersinia bacteria are relatively quickly inactivated by oxidizing agents such as hydrogen peroxide and potassium permanganate solutions.

Pathogenesis
Y. pestis is the causative agent of plague. The disease caused by Y. enterocolitica is called Yersiniosis.

Y. pseudotuberculosis sometimes but rarely causes disease.

Yersinia may be associated with Crohn's disease, an inflammatory autoimmune condition of the gut. Iranian sufferers of Crohn's disease were more likely to have had earlier exposure to refrigerators at home, consistent with Yersinia's unusual ability to thrive at low temperatures.

Yersinia is implicated as one of the causes of reactive arthritis worldwide.

Also associated with pseudoappendicitis, which is an incorrect diagnoses of appendicitis due to a similar presentation.

History
Yersinia pestis, the first described species, was identified in 1894 by A.E.J. Yersin, a Swiss bacteriologist, and Kitasato Shibasaburō, a Japanese bacteriologist. It was formerly described as Pasteurella pestis (known trivially as the plague-bacillus) by Lehmann and Neumann in 1896. In 1944, van Loghem reclassified the species P. pestis and P. rondentium into a new genus Yersinia. Following the introduction of the Bacteriological code, it was accepted as valid in 1980

treatment
the best treatment is a combination from streptomycin and tetracycline in case of failure of monotherapy by streptomycin or tetracycline.