Yersinia
Yersinia is a genus of bacteria in the family Yersiniaceae. "Yersinia" species are Gram-negative, coccobacilli 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 by protozoonotic mechanisms, since "Yersinia" species 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 also to actively proliferate at temperatures as low as 1–4 °C (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. Genetics. Database. The creation of YersiniaBase, a data and tools collection for the reporting and comparison of "Yersinia" species genome sequence data, was reported in January 2015. The provisional representation of species addressed by the resource has been indicated in the TaxBox on this page by a superscript 'yb' beside the species name. Development of YersiniaBase was funded by the University of Malaya and the Ministry of Education, Malaysia. Pathogenesis. "Y. pestis" is the causative agent of plague. The disease caused by "Y. enterocolitica" is called yersiniosis . "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 its unusual ability to thrive at low temperatures. "Yersinia" is implicated as one of the causes of reactive arthritis worldwide. Also, the genus is associated with pseudoappendicitis, which is an incorrect diagnosis of appendicitis due to a similar presentation. History. "Y. pestis", the first known 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.