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Yersinia
A group of bacteria that appear rod-like under the microscope and include Yersinia pestis (the cause of the bubonic and pneumonic plague), Yersinia entercolitica (the cause of a disease called yersinosis), and Yersinia pseudotuberculosis (which causes a condition called mesenteric adenitis, particularly in immunocompromised patients). Both Y. entercolitica and Y. pseudotuberculosis have also been implicated in a viral form of arthritis. Infection with Yersinia bacteria can be treated with antibiotics. Yersinia is named after the Swiss bacteriologist Alexandre-Emile-Jean Yersin (1863-1943) who identified it in 1894 after a trip to Hong Kong looking for the agent that was killing thousands of people in southern China. Since the bacteria was also discovered at the same time by the Japanese bacteriologist Shibasaburo Kitasako, Yersinia could well have been named after him.
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A genus of motile and nonmotile, non-spore-forming bacteria (family Enterobacteriaceae) containing Gram-negative, unencapsulated, ovoid to rod-shaped cells; Y. are nonmotile at 37°C, but some species are motile at temperatures below 30°C; motile cells are peritrichous; citrate is not used as a sole source of carbon; these organisms are parasitic on humans and other animals; the type species is Y. pestis. [A. J. E. Yersin, Swiss bacteriologist, 1862–1943]
- Y. enterocolitica a bacterial species that causes yersiniosis in humans; it is found in the feces and lymph node s of sick and healthy animals, including humans, in material likely to be contaminated with feces, and in the cadavers of cattle, rabbits, hares, dogs, guinea pig s, horses, monkeys, pigs, and sheep; it replicates at refrigerator temperatures and has been associated with contamination of blood and blood products.
- Y. frederiksenii reclassified from Y. enterocolitica; rare cause of enterocolitis in humans.
- Y. intermedia reclassified from Y. enterocolitica; rare cause of enterocolitis in humans.
- Y. kristensenii reclassified from Y. enterocolitica; pathogenicity uncertain.
- Y. pestis a bacterial species causing plague in humans, rodents, and many other mammalian species and transmitted from rat to rat and from rat to humans by the rat flea, Xenopsylla; it is the type species of the genus Y.. SYN: Kitasato bacillus, Pasteurella pestis, plague bacillus.
- Y. pseudotuberculosis a bacterial species causing pseudotuberculosis in birds, rodents, and, rarely, in humans. SYN: Pasteurella pseudotuberculosis.

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yer·sin·ia yər-'sin-ē-ə n
1) cap a genus of gram-negative bacteria of the family Enterobacteriaceae that includes several important pathogens (as the plague bacterium, Y. pestis) affecting animals and humans and formerly included in the genus Pasteurella see PLAGUE (2)
2) any bacterium of the genus Yersinia
Yer·sin yer-san Alexandre-Émile-John (1863-1943)
French bacteriologist. Yersin studied bacteriology under Émile Roux in Paris and Robert Koch in Berlin. Later, in Hong Kong, he and Kitasato Shibasaburo independently discovered the plague bacillus at about the same time. In 1944 the genus Yersinia containing the plague bacillus (Y. pestis) was named after Yersin.

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n.
a genus of aerobic or facultatively anaerobic Gram-negative bacteria that are parasites of animals and humans. Y. pestis causes bubonic plague; Y. enterocolitica causes intestinal infections.

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Yer·sin·ia (yər-sinґe-ə) [Alexandre J.E. Yersin, Swiss bacteriologist in France, 1863–1943] a genus of gram-negative bacteria of the family Enterobacteriaceae, consisting of facultatively anaerobic, non–spore-forming, nonencapsulated straight rods to coccobacilli; organisms are nonmotile at 37°C, but most species are motile by means of peritrichous flagella below 30°C. It contains the organism responsible for bubonic plague (see Y. pestis) and other species that cause gastroenteritis and mesenteric lymphadenitis. Numerous serovars based on the presence of an O antigen have been described. The type species is Y. pesґtis.

Medical dictionary. 2011.