ABSTRACT
1. Strains of Yearsinia enterocolitica, Y. intermedia, Y frederiksenii and Y. kristensenii from non-human sources were examined for virulence factors. Four of these strains were positive for autoagglutination, three were calcium dependent at 37-C, three produced lipase, five had the ability to bind Congo red, six had pyrazinamidase activity, and two had a 42 MDa plasmid. 2. One strain (Y. enterocolitica 0:5) was lethal for mice and had the ability to invade guinea pig eyes and HeLa cells. After inoculation of mice by the intravenous route, this strain was isolated from the cecum. The spleen, liver, kidneys and lymph nodes presented necrosis. After intragastric inoculation, the strain was isolated from all of the organs and tissues examined. 3. Three of the remaining strains invaded HeLa cells but none caused guinea pig conjunctivitis. 4. After intragastric inoculation, all the strains were isolated from the cecum but disappeared between dys 3 and 6. After intravenous infection, three strains produced necrosis of the spleen and were more invasive, eliciting infection in various organs. The remaining strains caused hypertrophy and hyperplasua of Peyer's patches and/or lymph nodes. 5. These results indicate that Y. enterocolitica 0:5 can be considered as virulent as typical European Y. enterocolitica strains. The remaining strains perphaps induce a weak immune response independent of virulence factors