Abstract
A serotype 4a strain of Yersinia pseudotuberculosis lacking the virulence plasmid pYV (pYV- strain) was isolated from the mesenteric lymph nodes but not from the stool or the appendix of a 10-year-old girl with a diagnosis of acute mesenteric lymphadenitis. Microscopically, reticulocytic abscess and lymphadenitis were persent in the enlarged mesenteric lymph nodes. Antibody against the isolate was detected in the serum. The isolate was negative for the presence of plasmid pYV and plasmid pYV-mediated properties, including autoagglutination and calcium dependency, but was positive for chromosome-mediated properties, including invasion into HeLa cells and tissues of mice and the Serény test. Mice were orally infected with this pYV- strain, and rapid elimination from the intestine occurred 14 days later. Hence, the potential to inhibit the phagocytosis encoded by plasmid pYV was lacking. As the pYV- strain was recovered from the mesenteric lymph nodes and the spleen, the invasiveness was encoded by chromosomal genes. The count of the pYV- strain in the mesenteric lymph nodes increased to 10(4.6) cells per g within 4 days. These findings suggest that pYV- Y. pseudotuberculosis was the causative agent of acute mesenteric lymphadenitis in the absence of gastroenteritis.