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INTRODUCTION

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The genus Yersinia is a member of the Enterobacteriaceae family that includes 11 species and is an important cause of foodborne illness. Yersinia enterocolitica is a small pleomorphic gram-negative, non–spore-forming coccobacillus that has been classified into 6 biotypes and more than 60 serotypes. The serotypes most often associated with human disease are 0:3, 0:5, 0:8, 0:9, 0:13, and 0:27. Human illness can occur after consumption of Y enterocolitica–contaminated food, animal waste, and unchlorinated water. This organism may survive and grow during refrigerated storage. Human illness ranges from self-limited enteritis to potentially life-threatening systemic infection.

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PATHOGENESIS AND EPIDEMIOLOGY

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Yersinia enterocolitica is an invasive organism and causes disease by tissue destruction. Pathogenic properties include chromosomally mediated effects such as invasion attachment to host cells, iron complexing and uptake, and enterotoxin production. Plasmid-mediated mechanisms include production of outer membrane antigens, calcium dependency for growth, and autoagglutination. Invasion and penetration of the mucosa occur in the ileum, followed by multiplication in Peyer’s patches.

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Drainage into the mesenteric lymph nodes can lead to systemic infection or mesenteric adenitis. The enterotoxin produced by Y enterocolitica appears to play a minor role in causing disease because diarrheal illness can occur in the absence of enterotoxin production. In addition, the toxin appears to be produced only at temperatures lower than 30°C. The plasmid-mediated outer membrane antigens are associated with bacterial resistance to opsonization and neutrophil phagocytosis.

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One unique property of Y enterocolitica is its inability to chelate iron. Iron is an essential factor for growth of most bacteria. Bacteria produce and release iron-binding chelators known as siderophores that extract iron from transferrin. Y enterocolitica does not produce siderophores but has receptors for them and can use siderophores produced by other bacteria including the gastrointestinal flora (eg, deferoxamine produced by Streptomyces pilosus). Iron overload substantially increases the pathogenicity of the organism, perhaps through attenuation of the bactericidal activity of the serum. However, to establish extraintestinal infection, an exogenous siderophore (eg, a chelating agent such as deferoxamine) or excess iron is required. It is for this reason that Y enterocolitica bacteremia and other systemic infections are more often seen in patients with iron overload and those receiving chelation therapy including patients with thalassemia major with hemosiderosis and some patients with sickle cell disease.

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Yersinia enterocolitica has been isolated from humans worldwide, but most commonly in cooler climates. The organism has a large animal reservoir, including cattle, sheep, swine, dogs, cats, horses, rodents, and lagomorphs. Streams, lakes, and drinking water have all been contaminated. The most common mode of transmission is ingestion of contaminated food, milk, or water. Person-to-person transmission has not been conclusively proven but probably occurs. Seasonal isolation rates of Yersinia indicate that it is more prevalent as a cause of enteritis in winter months in the United States. Because pigs are often infected, persons who eat or handle pork are at risk ...

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